Alumina-silica-based fiber, ceramic fiber, ceramic fiber complex, retaining seal material, production method thereof, and alumina fiber complex production method

ABSTRACT

A holding seal material which has alumina-silica based fibers aggregated into a mat shape as a constituent element. The holding seal material is placed in a gap between a ceramic body capable of allowing a fluid to flow through the inside thereof and a metal shell covering the outer circumference of the ceramic body. In the holding seal material, a crystallization rate is made different depending on portions of the holding seal material. An outer portion of the holding seal material disposed with respect to the metal shell is crystallized at a lower rate than an inner portion of the holding seal material disposed with respect to the ceramic body.

TECHNICAL FIELD

The present invention relates to an alumina-silica based fiber, aceramic fiber, a ceramic fiber aggregation, a holding seal material andmanufacturing methods thereof, as well as a manufacturing method ofalumina fiber aggregation.

BACKGROUND ART

Recently, there has been a problem that particulates contained inexhausted gas discharged from combustion engines of vehicles such asbuses, trucks, construction machines and the like affect the environmentand the human body.

There have been various ceramic filters which allow the exhausted gas topass through porous ceramic, thereby capturing the particulates in theexhausted gas and purifying the exhausted gas.

As one example of such ceramic filters, there is used a honeycomb filter30 in which a plurality of porous ceramic members 40 shown in FIG. 16are bound by means of an adhesive layer 34 to constitute a column-shapedceramic block 35, and a seal material layer 33 is formed around thecolumn-shaped ceramic block 35. Moreover, as shown in FIG. 17, thisporous ceramic member 40 is provided with a number of through holes 42aligned in the longitudinal direction so that each partition wall 43separating the through holes 42 from each other functions as a filter.

In other words, as shown in FIG. 17( b), with respect to each of thethrough holes 42 formed in the porous ceramic member 40, either of theends on the inlet side or outlet side of the exhaust gas is sealed by afilling material 41 so that the exhaust gas, flown into a through hole42, is always allowed to flow out through another through hole 42 afterhaving passed through this partition wall 43 that separates throughholes 42; thus, when the exhaust gas passes through the partition wall43, particulates thereof are captured by the partition wall 43 so thatthe exhaust gas is purified.

Moreover, a seal material layer 33 is formed on the outercircumferential portion so that one portion thereof is formed to preventthe exhaust gas from leaking from the through holes 42 exposed to theoutside of the porous ceramic member 40.

With respect to a non-oxide-based ceramic material constituting theporous ceramic member 40 of this type, silicon carbide, which isexcellent in heat resistance, and easily subjected to a recoveringprocess and the like, is used in various vehicles such as large-sizevehicles and vehicles having diesel engines.

Further, in addition to the above-mentioned particulates, theabove-mentioned exhaust gas contains CO, NOx, HC, etc., and in order toremove these substances from the exhaust gas, an exhaust gas purifyingcatalyst converter, which has virtually the same shape as theabove-mentioned honey comb filter 30 with a catalyst such as platinumdeposited therein, has been proposed.

Moreover, in recent years, studies have been conducted on the nextgeneration clean power sources which do not use petroleum as the powersource, and among these, for example, fuel cells have been considered tobe a very prospective power source.

The fuel cells, which utilize electricity that is obtained when hydrogenand oxygen react with each other to form water as a power source, havean arrangement in which oxygen is directly taken from the air whilemethanol, gasoline and the like are modified and utilized to providehydrogen, and upon modifying these methanol, gasoline and the like, anexhaust gas purifying catalyst converter, which has virtually the sameshape as the above-mentioned honey comb filter 30 with a copper-basedcatalyst deposited therein, has been utilized.

Generally, these honeycomb filter 30, an exhaust gas purifying catalystconverter, a catalyst converter for a fuel cell and the like are placedinside a cylinder-shaped metal shell, and used, and in this case, thereis a gap between the honeycomb filter 30, the exhaust gas purifyingcatalyst converter or the catalyst converter for a fuel cell and theabove-mentioned metal shell, and in order to fill the gap, a holdingseal materials 50 shown in FIG. 18 is interpolated therein.

As shown in FIG. 18, the holding seal material 50 is provided with aconvex fitting section 52 placed on one of the shorter sides of a basematerial portion 51 having a virtually rectangular shape, and a concavefitting section 53 placed on the other shorter side.

The convex fitting section 52 and the concave fitting section 53 arejust fitted to each other when the holding seal material 50 is woundaround the outer circumference of the honeycomb filter 30; thus, it ispossible to prevent the holding seal material 50 from deviation.

Conventionally, the holding seal material of this type has been formedthrough the following first through fourth methods.

In other words, in the first method for manufacturing theabove-mentioned holding seal material, first, a starting materialcontaining an alumina source and a silica source is heated toapproximately 2000° C., and subjected to a spinning process in a fusedstate, and then quickly cooled down to obtain ceramic fibers that hasvirtually the same alumina content and silica content. Then, a materialis produced by aggregating the above-mentioned ceramic fibers into a matshape. This material is stamped out by using a metal mold to manufactureholding seal materials.

In the second method for manufacturing the above-mentioned holding sealmaterial, first, a spinning stock solution containing an alumina sourceand a silica source is prepared, and by discharging this solutionthrough a nozzle, a precursor fiber having a true round shape in itscross-section is continuously obtained. Next, the long fiber of theprecursor fiber obtained through the above-mentioned spinning process issintered, and the resulting alumina-silica based fiber is then choppedinto short fibers having a predetermined length. Next, the short fibersthus obtained are put into a mold to form a fiber aggregation having amat shape. This fiber aggregation is stamped out by using a metal moldto manufacture holding seal materials.

Moreover, in the third method for manufacturing the above-mentionedholding seal material, a spinning stock solution, preliminarily preparedfor use in an inorganic salt method, is supplied to a centrifugalnozzle, and the spinning stock solution is blown out of the nozzle by acentrifugal force exerted on the centrifugal nozzle to form precursorfibers. Next, the resulting precursor fibers are aggregated into a matshape, and this mat-shaped aggregation is stamped out by using a metalmold to manufacture holding seal materials.

In the fourth method for manufacturing the above-mentioned holding sealmaterial, first, an alumina fiber stock solution (alumina-silica fiberstock solution) is subjected to a spinning process to form a continuouslong-fiber precursor, and an alumina long fiber is manufactured bysintering this continuous long-fiber precursor.

Next, after this alumina long fiber has been cut into alumina shortfibers, these alumina short fibers are collected, untied, and laminated,and this is then pressed to form an alumina fiber aggregation having amat shape.

Then, this mat-shaped aggregation is stamped out into a predeterminedshape to manufacture holding seal materials.

The holding seal material, thus manufactured, is wound on the outercircumferential face of the above-mentioned honeycomb filter, theexhaust gas purifying catalyst converter or the catalyst converter for afuel cell, and this is then housed in a metal shell; and in such ahoused state, since the holding seal material is compressed in thethickness direction so that a repulsive force (face pressure) resistingagainst the compressing force is exerted in the holding seal material.The repulsive force thus exerted makes it possible to hold elements,such as the honeycomb filter, the exhaust gas purifying catalystconverter and the catalyst converter for a fuel cell, inside theabove-mentioned metal shell.

In the case where the honeycomb filter, the exhaust gas purifyingcatalyst converter, the catalyst converter for a fuel cell, etc. arehoused inside the above-mentioned metal shell through a press-fittingmethod, a metal cylinder member having an O-letter shape in itscross-section is used, and when these are housed inside thereof by usinga canning method, a clamshell, which is formed by dividing a metalcylinder member having an O-letter shape in its cross-section into aplurality of pieces along the axis-line direction thereof, is used.Moreover, in addition to this method, a metal shell, which uses atightening method in which welding, bonding and bolt-fastening processesare carried out by using a metal cylinder-shaped member having aC-letter shape or a U-letter shape in its cross-section, is alsoutilized.

However, with respect to the holding seal material manufactured throughthe first method, since this member is subjected to vibration and hightemperatures of such as exhaust gas, when it is used, the face pressureis gradually lowered as time elapses, resulting in degradation in theholding property and sealing property of the catalyst carrier in acomparatively early period of time.

Moreover, with respect to the holding seal material manufactured by thefirst method, properties for securely holding the honeycomb filter, theexhaust gas purifying catalyst converter, the catalyst converter for afuel cell, etc. for a long period of time are required; however, theconventional ceramic fibers, manufactured through the above-mentionedfusing method, has a very low level of crystallization rate (mulliterate), that is, less than 1% by weight, in addition to its high level ofamorphous components. For this reason, when the resulting fibers aresubjected to high temperatures for a long time, thermal shrinkage occursas crystallization advances, resulting in brittleness in the fibers.Therefore, the holding seal material, manufactured by using thesefibers, fails to provide a sufficiently high initial face pressure, andcauses high degradation with time in the face pressure during theapplication.

In order to solve these problems, a method for increasing thecrystallization rate of the ceramic fibers to approximately 10% byweight has been proposed; however, in this case, hardening of the fiberscauses degradation in the elasticity and flexibility of the holding sealmaterial and the subsequent degradation in the sealing property.

Moreover, with respect to the holding seal material manufactured by thesecond method, properties for securely holding the honeycomb filter, theexhaust gas purifying catalyst converter, the catalyst converter for afuel cell, etc. for a long period of time are required; however, thealumina-silica based fiber having a round shape in its cross-section,manufactured in the second method, tends to lose its flexibility tobecome brittle, and is easily broken, when exposed to high temperaturesfor a long time. Therefore, the holding seal material manufactured bythese fibers is susceptible to degradation with time in the facepressure.

Furthermore, with respect to the holding seal material manufactured bythe third method, when the formation of ceramic fibers is carried out byusing the blowing method, the basis weight (weight per unit area) of themat-shaped aggregation comes to have a higher positional dependence.

In other words, the degree of aggregation in fibers is not constant withthe result that when the position at which the mat-shaped aggregation isstamped out differs, the face pressure value of the resulting holdingseal material tends to differ. Consequently, it has not been possible toobtain a holding seal material having excellent stability in quality.

Here, in the alumina fiber aggregation formed by the above-mentionedfourth method, alumina short fibers, used for the alumina fiberaggregation, fail to have sufficiently high mechanical strength, andhave comparatively great dispersions, with the result that the initialface pressure of the alumina fiber aggregation becomes insufficient, andthe degradation with time in the face pressure of the above-mentionedalumina fiber aggregation is comparatively large; therefore, there havebeen demands for improvements.

Here, “the initial face pressure” refers to a face pressure of analumina fiber aggregation in a state where neither load nor heat isapplied thereto.

The present invention has been devised to solve the above-mentionedproblems, and an object of a first group of the present invention is toprovide a holding seal material which has a high initial face pressure,and is less susceptible to degradation with time in the face pressure,to provide an alumina-silica based fiber excellent in mechanicalstrength and suitable for obtaining the above-mentioned holding sealmaterial and a manufacturing method thereof, and also to provide amanufacturing method of alumina-silica based fibers capable of securelyobtaining the above-mentioned alumina-silica based fiber excellent inmechanical strength easily.

Moreover, an object of a second group of the present invention is toprovide a holding seal material which has a high initial face pressure,and is less susceptible to degradation with time in the face pressure,with excellent sealing properties, and a catalyst converter, and also toprovide a manufacturing method of a holding seal material which issuitable for obtaining the above-mentioned holding seal material.

Furthermore, an object of a third group of the present invention is toprovide a holding seal material which is less susceptible to degradationwith time in the face pressure, and also to provide a manufacturingmethod of alumina-silica based fibers that are used for theabove-mentioned holding seal material.

Furthermore, an object of a fourth group of the present invention is toprovide a holding seal material excellent in quality stability, and alsoto provide a manufacturing method of a holding seal material which issuitable for obtaining the above-mentioned holding seal material.

Furthermore, an object of a fifth group of the present invention is toprovide a holding seal material which is less susceptible to degradationwith time in face pressure, and also to provide a manufacturing methodof a holding seal material which is suitable for the above-mentionedholding seal material, a ceramic fiber aggregation and ceramic fibersthereof.

Furthermore, an object of a sixth group of the present invention is toprovide a manufacturing method of an alumina fiber aggregation which hasalumina short fibers having high strength with small dispersions so thatit provides a sufficiently high initial face pressure, and is lesssusceptible to degradation with time.

SUMMARY OF THE INVENTION

The present inventors studied hard so as to solve the problems for theabove-mentioned first group of the present invention, and after a numberof processes of trial and error, fortunately, made it possible toproduce alumina-silica based fibers excellent in mechanical strength.The alumina-silica based fibers thus produced generally have a blackishcolor, and have characteristics that are clearly different from those ofwhite, transparent alumina-silica based fibers that have been generallyknown. The present inventors further studied hard so as to find thecause of generation of the color which is different from the color ofthe generally-known fibers. As a result, they found that as the residualcarbon content in the fibers increased, the fibers came to have ablackish color, and that the presence of the residual carbon contentimproved the mechanical strength. Thus, based upon these findings, thepresent inventors further studied hard, and finally arrived at thefollowing first group of the present invention.

That is, the invention according to the first group of the presentinvention summarizes an alumina-silica based fiber which presents ablackish color.

The invention according to the first group of the present inventionsummarizes an alumina-silica based fiber which presents a blackish colorderived from a carbon component.

The invention according to the first group of the present inventionsummarizes an alumina-silica based fiber which has a residual carboncontent of 1% by weight or more, presents a blackish color derived fromits residual carbon component, and has a fiber tensile strength of 1.2GPa or more, a fiber bending strength of 1.0 GPa or more and a fracturetoughness of 0.8 MN/m^(3/2) or more.

The invention according to the first group of the present inventionsummarizes a manufacturing method of alumina-silica based fibers,including: a spinning step of obtaining precursor fibers by using aspinning stock solution of the alumina-silica based fibers for aninorganic salt method as a material; and a firing step of heating theabove-mentioned precursor fibers under an environment which makes itdifficult to carry out an oxidizing reaction on the carbon componentcontained in the above-mentioned precursor fibers, thereby sintering theabove-mentioned precursor fibers.

The invention according to the first group of the present invention,wherein the above-mentioned precursor fiber is heated at a temperatureof 1000 to 1300° C. under a nitrogen atmosphere.

The invention according to the first group of the present invention,wherein the carbon component contained in the above-mentioned precursorfiber is derived from an organic polymer added to the above-mentionedspinning stock solution of the alumina-silica based fiber as afiber-drawing property applying agent.

The invention according to the first group of the present inventionsummarizes a holding seal material which has alumina-silica basedfibers, according to any of claims 1 to 3, aggregated into a mat shapeas a constituent element, and is placed in a gap between a ceramic bodycapable of allowing a fluid to flow through the inside thereof and ametal shell covering the outer circumference of the ceramic body.

The invention according to the first group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

In order to solve the problem for the second group of the presentinvention, the invention according to the second group of the presentinvention summarizes a holding seal material which has a fiberaggregation of alumina-silica based fibers aggregated into a mat shapeas a constituent element, and is placed in a gap between a ceramic bodycapable of allowing a fluid to flow through the inside thereof and ametal shell covering the outer circumference of the ceramic body,wherein a crystallization rate in a portion on a first face side isdifferent from that in a portion on a second face side.

The invention according to the second group of the present inventionsummarizes a holding seal material which has a fiber aggregation ofalumina-silica based fibers aggregated into a mat shape as a constituentelement, and is placed in a gap between a ceramic body capable ofallowing a fluid to flow through the inside thereof and a metal shellcovering the outer circumference of the ceramic body, wherein

a crystallization rate is gradually increased from a first face sidetoward a second face side.

The invention according to the second group of the present invention,including a sheet of fiber aggregation, wherein the crystallization rateof the fiber aggregation is gradually increased from the first face sidetoward the second face side.

The invention according to the second group of the present invention,wherein the difference between the crystallization rates in the portionon the first face side and that in the portion on the second face sideis 3% by weight or more.

The invention according to the second group of the present invention,wherein the crystallization rate in the portion on the first face sideis 0 to 1% by weight, and the crystallization rate in the portion on thesecond face side is 1 to 10% by weight.

The invention according to the second group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

The invention according to the second group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein a crystallization rate is made differentdepending on portions.

The invention according to the second group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

The invention according to the second group of the present inventionsummarizes a manufacturing method of a holding seal material, including:a spinning step of obtaining precursor fibers by using a spinning stocksolution of ceramic fibers as material; a laminating step of laminatingthe above-mentioned precursor fibers to form a mat-shaped fiberaggregation; and a firing step of sintering the above-mentioned fiberaggregation so as to provide a difference between a firing temperatureon a first face side and that on a second face side.

The invention according to the second group of the present invention,wherein the difference between the above-mentioned firing temperaturesis set to 100° C. or more.

The invention according to the second group of the present invention,wherein the firing temperature on the first face side is set to 800 to1100° C., and the firing temperature on the second face side is set to1100 to 1400° C.

The invention according to the second group of the present inventionsummarizes a catalyst converter comprising: a catalyst carrier; acylinder-shaped metal shell covering the outer circumference of thecatalyst carrier; and a holding seal material placed in a gap betweenthese elements, and having alumina-silica based fibers aggregated into amat shape as a constituent element, wherein the above-mentioned holdingseal material is placed in the above-mentioned gap in such a state thata first face side having a relatively small crystallization rate is madein contact with the above-mentioned metal shell, and a second face sidehaving a relatively large crystallization rate is made in contact withthe above-mentioned catalyst carrier.

In order to solve the problem for the third group of the presentinvention, the invention according to the third group of the presentinvention summarizes a holding seal material which has alumina-silicabased fibers aggregated into a mat shape as a constituent element, andis placed in a gap between a ceramic body capable of allowing a fluid toflow through the inside thereof and a metal shell covering the outercircumference of the ceramic body, wherein the above-mentionedalumina-silica based fiber has a non-circular shape in itscross-section.

The invention according to the third group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein the above-mentioned alumina-silica based fiberhas a deformed shape in its cross-section.

The invention according to the third group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein the above-mentioned alumina-silica based fiberhas a flat shape in its cross-section.

The invention according to the third group of the present invention,wherein the above-mentioned alumina-silica based fiber has asubstantially elliptical or cocoon shape in its cross-section.

The invention according to the third group of the present invention,wherein the above-mentioned alumina-silica based fiber is a hollowfiber.

The invention according to the third group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

The invention according to the third group of the present inventionsummarizes a manufacturing method of alumina-silica based fibers used ina holding seal material including: a spinning step of obtainingprecursor fibers by discharging a spinning stock solution containing asolution of aluminum salt water, silica sol and an organic polymerthrough a nozzle; and a firing step of heating and sintering theabove-mentioned precursor fibers, wherein dried hot air is blown to theabove-mentioned precursor fibers immediately after having beendischarged from the discharging section of the above-mentioned nozzlehaving a non-circular shape in its cross-section.

The invention according to the third group of the present invention,wherein the above-mentioned dried hot air is blown in a forwarddirection with respect to the discharging direction of theabove-mentioned precursor fiber.

The invention according to the third group of the present invention,where in a water-soluble plasticizer is preliminarily added to theabove-mentioned spinning stock solution.

Moreover, in order to solve the problem for the fourth group of thepresent invention, the invention according to the fourth group of thepresent invention summarizes a holding seal material which hasalumina-silica based fibers aggregated into a mat shape as a constituentelement, and is placed in a gap between a ceramic body capable ofallowing a fluid to flow through the inside thereof and a metal shellcovering the outer circumference of the ceramic body, wherein thedispersion of fiber diameter in the above-mentioned alumina-silica basedfiber is within ±3 μm.

The invention according to the fourth group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein the dispersion of fiber length in theabove-mentioned alumina-silica based fiber is within ±4 mm.

The invention according to the fourth group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein the dispersion of fiber diameter in theabove-mentioned alumina-silica based fiber is within ±3 μm, and thedispersion of fiber length in the above-mentioned alumina-silica basedfiber is within ±4 mm.

The invention according to the fourth group of the present invention,wherein the content of shots is 3% by weight or less.

The invention according to the fourth group of the present inventionsummarizes a holding seal material which has alumina-silica based fibersaggregated into a mat shape as a constituent element, and is placed in agap between a ceramic body capable of allowing a fluid to flow throughthe inside thereof and a metal shell covering the outer circumference ofthe ceramic body, wherein the average fiber diameter of theabove-mentioned alumina-silica based fiber is 5 to 15 μm, the dispersionof fiber diameter therein is within ±3 μm, the average fiber lengththereof is 5 to 20 mm, the dispersion of fiber length therein is within±4 mm, and no shots are contained therein.

The invention according to the fourth group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

The invention according to the fourth group of the present inventionsummarizes a manufacturing method of a holding seal material, including:a spinning step of obtaining long precursor fibers by continuouslydischarging a spinning stock solution containing a solution of aluminumsalt water, silica sol and an organic polymer through a nozzle; acutting step of chopping the above-mentioned long fibers into apredetermined length to obtain short fibers; a molding step of allowingthe above-mentioned short fibers to aggregate three-dimensionally,thereby forming into a mat-shaped fiber aggregation; and a firing stepof heating and sintering the above-mentioned mat-shaped fiberaggregation.

Moreover, the inventors of the present invention studied hard to solveproblems for the fifth group of the present invention.

As a result, it has been found that when an external load is applied fora long time in a manner so as to compress the fiber aggregation, theceramic fibers constituting the fiber aggregation tend to slide on oneanother to cause dispersions, resulting in degradation in the facepressure of the fiber aggregation. Therefore, the inventors of thepresent application have attempted to solve the problems of sliding anddispersions among the fibers by applying any means to obtain betterresults, and take portions at which fibers are adjacent to each otherwith overlapped parts into consideration. Thus, they have furtherstudied energetically to improve such portions, and finally have reachedthe following fifth group of the present invention.

The invention according to the fifth group of the present inventionsummarizes a holding seal material which has ceramic fibers aggregatedinto a mat shape as a constituent element, and is placed in a gapbetween a ceramic body capable of allowing a fluid to flow through theinside thereof and a metal shell covering the outer circumference of theceramic body, wherein the ceramic fibers are partially bonded to eachother by a ceramic adhesive.

The invention according to the fifth group of the present invention,wherein the above-mentioned ceramic comprises a substance whichconstitutes the above-mentioned ceramic fiber.

The invention according to the fifth group of the present invention,wherein the above-mentioned ceramic fibers are alumina-silica basedfibers, and the above-mentioned ceramic adhesive has alumina as a maincomponent.

The invention according to the fifth group of the present invention,wherein 1 to 8% by weight of the above-mentioned ceramic adhesive iscontained therein.

The invention according to the fifth group of the present invention,wherein the above-mentioned ceramic body includes a catalyst carrier,and the above-mentioned holding seal material is used as a holding sealmaterial for a catalyst converter.

The invention according to the fifth group of the present inventionsummarizes a manufacturing method of a holding seal material, including:a spinning step of obtaining precursor fibers by using a spinning stocksolution of ceramic fibers as a material; a firing step of heating andsintering the above-mentioned precursor fibers; a molding step ofallowing thus obtained ceramic fibers to aggregate three-dimensionally,thereby forming into a mat-shaped aggregation; and bonding step ofbonding the ceramic fibers forming the above-mentioned aggregation byusing a ceramic adhesive.

The invention according to the fifth group of the present invention,wherein in the above-mentioned bonding step, after the material solutionof the above-mentioned ceramic adhesive has been supplied between theceramic fibers forming the above-mentioned aggregation, theabove-mentioned aggregation is heated to sinter specific components inthe above-mentioned material solution so as to be formed into ceramics.

The invention according to the fifth group of the present inventionsummarizes the invention, wherein in the above-mentioned bonding step,after the above-mentioned aggregation has been impregnated with awater-soluble metal solution, which is the above-mentioned materialsolution, having a low viscosity, the above-mentioned aggregation isdried and heated so that the metal component in the above-mentionedsolution is sintered to be formed into ceramics.

The invention according to the fifth group of the present invention,wherein the above-mentioned water-soluble metal solution is supplied byan amount of 1 to 10% by weight of the above-mentioned aggregation.

The invention according to the fifth group of the present invention,wherein the above-mentioned spinning stock solution of the ceramicfibers is a spinning stock solution of alumina-silica based fibersprepared by using an inorganic salt method, and the above-mentionedwater-soluble metal solution is a water solution containing aluminumions.

The invention according to the fifth group of the present inventionsummarizes a manufacturing method of a holding seal material, including:a spinning step of obtaining precursor fibers by using a spinning stocksolution of ceramic fibers as a material; a molding step of allowing theabove-mentioned precursor fibers to aggregate three-dimensionally,thereby forming into a mat-shaped aggregation; a liquid substancesupplying step of allowing a liquid substance capable of being a ceramicadhesive later to adhere to portions at which the above-mentionedprecursor fibers forming the above-mentioned aggregation are overlappedadjacent to each other; and a firing step of heating the above-mentionedaggregation to sinter the above-mentioned precursor fibers and theabove-mentioned liquid substance.

The invention according to the fifth group of the present invention,wherein in the above-mentioned liquid substance supplying step, theaggregation including the above-mentioned precursor fibers ofalumina-silica based fibers is put in a highly moistened environmentwith high moisture.

The invention according to the fifth group of the present invention,wherein in the above-mentioned liquid substance supplying step, anon-aqueous liquid substance containing an inorganic element containedin the above-mentioned alumina-silica based fiber is atomized andsupplied to the aggregation including the precursor fibers of thealumina-silica based fibers.

The invention according to the fifth group of the present invention,wherein a cutting step of chopping the long fibers of theabove-mentioned precursor fibers into a predetermined length to obtainshort fibers is carried out between the above-mentioned spinning stepand the above-mentioned molding step.

The invention according to the fifth group of the present inventionsummarizes a ceramic fiber aggregation wherein three-dimensionallyaggregated ceramic fibers are partially bonded to each other by aceramic adhesive.

The invention according to the fifth group of the present inventionsummarizes a ceramic fiber aggregation comprising ceramic fibers havinga branched structure.

The invention according to the fifth group of the present inventionsummarizes a ceramic fiber having a branched structure.

Moreover, in order to solve the problem for the sixth group of thepresent invention, the invention according to the sixth group of thepresent invention summarizes a manufacturing method of an alumina fiberaggregation, including: a spinning step of obtaining a continuouslong-fiber precursor by using an alumina fiber stock solution used in aninorganic salt method as a material; a chopping step of cutting theabove-mentioned continuous long-fiber precursor into short-fiberprecursors; a mat preparing step of preparing a mat-shaped short fiberprecursor by using thus obtained short-fiber precursor; and a firingstep of firing the above-mentioned mat-shaped short fiber precursor tomanufacture an alumina fiber aggregation.

The following description will be given of “operations” of the firstgroup of the present invention.

In accordance with the inventions of the first group of the presentinvention, since black colored alumina-silica based fibers are generallyexcellent in the mechanical strength, the application of these fibersmakes it possible to achieve a holding seal material that has a highinitial face pressure, and is less susceptible to degradation with timein the face pressure.

Here, when the fiber tensile strength, fiber bending strength andfracture toughness are the above-mentioned values or more, it ispossible to achieve alumina-silica based fibers that have very highresistance against tension and bending, and are flexible andunbreakable. Therefore, it becomes possible to improve the initial facepressure, and also to securely prevent degradation with time in the facepressure. Moreover, the alumina-silica based fibers that are blackcolored, contain carbon components in the fibers thereof, and since thecrystallization is allowed to progress in the entire alumina-silicabased fibers, it becomes possible to achieve the excellent mechanicalstrength such as tensile strength.

In accordance with the invention of the first group of the presentinvention, it is possible to sinter the precursor fibers without causingoxidation in the carbon components in the precursor fibers. For thisreason, it is possible to allow much carbon components to remain in thefibers, and consequently to securely obtain fibers that are excellent inthe mechanical strength easily.

Here, since most of the carbon components in the precursor fibers arenormally burnt to disappear before the firing temperature has beenattained, the carbon components seldom remain in the alumina-silicabased fibers obtained through the firing step. However, in the casewhere the precursor fibers are heated under an environment that hardlyallows oxidizing reaction of the carbon components to progress, it isconsidered that carbon is allowed to remain in the fibers to beassembled into the ceramic skeleton to a certain degree.

In accordance with the invention in the first group of the presentinvention, an inexpensive nitrogen atmosphere is utilized as an inertatmosphere in which the firing step is carried out; therefore, itbecomes possible to cut manufacturing costs. Moreover, since the firingtemperature is set in the above-mentioned preferable range, it ispossible to obtain alumina-silica based fibers having high strengthstably.

When the heating temperature of the precursor fibers is less than 1000°C., the sintering step of the precursor fibers tends to becomeinsufficient, and in such a case, even when the residual carbon contentis sufficient, it becomes difficult to stably obtain alumina-silicabased fibers having high strength. In contrast, even when the heatingtemperature of the precursor fibers is set so as to exceed 1300° C.,this fails to especially increase the strength of the alumina-silicabased fibers, resulting in deterioration in economical efficiencyinstead of improvements.

In accordance with the invention according to the first group of thepresent invention, the above-mentioned organic polymer not only servesas a string-drawing-property applying agent, but also functions ascarbon sources that add carbon to the precursor fibers so as to allowthe alumina-silica based fibers to have appropriate strength. Therefore,it is not necessary to especially add carbon sources to the spinningstock solution in a separated manner, thereby making it possible toeliminate the necessity of greatly modifying the composition of thespinning stock solution. Thus, it is possible to preliminarily avoidimbalance in the stock solution composition, and consequently to preventdegradation in the basic physical properties in the alumina-silica basedfibers. Moreover, since no carbon source needs to be added, it becomespossible to reduce the manufacturing costs. Furthermore, since theabove-mentioned organic polymer is easily dispersed in the spinningstock solution evenly, the carbon sources are evenly dispersed in theprecursor fibers. Consequently, the resulting alumina-silica basedfibers are allowed to have an even residual carbon content, and tend tohave less irregularity in the mechanical strength.

In this case, since the organic polymer of this type is burned todisappear normally at a temperature of approximately 500 to 600° C.,nothing is left in the alumina-silica based fibers obtained through thefiring step. However, it is considered that, when the precursor fibersare heated under an environment that hardly allows the oxidizingreaction of carbon contents to progress, carbon constituting the organicpolymer is allowed to remain in the fibers, and assembled into theceramic skeleton to a certain degree.

In accordance with the invention according to the first group of thepresent invention, since the alumina-silica based fibers havingexcellent mechanical strength are used as the constituent elements, itbecomes possible to provide a holding seal material that has a highinitial face pressure, tends to have less degradation with time in theface pressure.

In accordance with the invention according to the first group of thepresent invention, since the alumina-silica based fibers havingexcellent mechanical strength are used as the constituent elements withthe ceramic body being composed of a catalyst carrier, and since theholding seal material is used as a catalyst converter-use holding sealmaterial, it becomes possible to provide a catalyst-converter-useholding seal material that has a high initial face pressure, and is lesssusceptible to degradation with time in the face pressure.

In other words, in accordance with the invention of the first group ofthe present invention, the holding seal material is provided as acatalyst-converter-use holding seal material that includesalumina-silica based fibers as its constituent elements, and is placedin a gap between the catalyst carrier and the metal shell that coversthe outer circumference of the catalyst carrier.

The following description will be given of “operations” of the secondgroup of the present invention.

In accordance with the invention according to the second group of thepresent invention, the crystallization rate on the portion on the firstface side is made different from the crystallization rate on the portionon the second face side. With this arrangement, the portion on the faceside that has a relatively high crystallization rate, and is excellentin the heat resistance is placed on a high-temperature side, and theportion on the face side that has a relatively low crystallization rate,and is excellent in the elasticity and flexibility is placed on alow-temperature side. Therefore, the fibers are made less susceptible tobrittleness on the high-temperature side, and on the low-temperatureside, it becomes possible to avoid the occurrence of a gap to the othermembers. Thus, it becomes possible to achieve a holding seal materialthat is excellent in the sealing property, in addition to the advantagesthat it has high initial face pressure, and is less susceptible todegradation with time in the face pressure.

In accordance with the invention according to the second group of thepresent invention, since the crystallization rate is gradually increasedfrom the first face side toward the second face side, the portion on thesecond face side that is excellent in the heat resistance can be placedon a high-temperature side, and the portion on the first face side thatis excellent in the elasticity and flexibility can be placed on alow-temperature side. Therefore, the fibers are made less susceptible tobrittleness on the high-temperature side, and on the low-temperatureside, it becomes possible to avoid the occurrence of a gap to the othermembers. Thus, it becomes possible to achieve a holding seal materialthat is excellent in the sealing property, in addition to the advantagesthat it has high initial face pressure, and is less susceptible todegradation with time in the face pressure.

In accordance with the invention according to the second group of thepresent invention, different from a structure constituted by a pluralityof sheets of fiber aggregations that have mutually differentcrystallization rates, it is possible to eliminate the necessity of thejobs for mutually superposing the fiber aggregations so as to be bondedto one another, and consequently to reduce the number of processes uponmanufacturing the device. Moreover, since it is possible to provide athinner structure in comparison with the laminated structure of aplurality of sheets, the resulting structure is comparatively easilyplaced in a narrow gap. Moreover, in comparison with the laminatedstructure of a plurality of sheets in which fluids might pass throughthe interface between the fiber aggregations, since no interface existsin such a single sheet structure of the third invention of the secondgroup of the present invention, it is not necessary to take the passageof fluid into consideration. Thus, it is possible to provide a structurethat is excellent in the sealing property.

In accordance with the invention according to the second group of thepresent invention, since the difference between the crystallization rateof the portion on the first face side and the crystallization rate ofthe portion on the second face side is set to 3% by weight or more sothat it becomes possible to securely improve the face pressurecharacteristics and the sealing property.

When the difference between the crystallization rate of the portion onthe first face side and the crystallization rate of the portion on thesecond face side is less than 3% by weight, the difference between thecrystallization rates of the two sides becomes too small, it may not beable to provide the target characteristics.

In accordance with the invention according to the second group of thepresent invention, the crystallization rate of the portion on the firstface side and the crystallization rate of the portion on the second faceside are respectively set in the above-mentioned desired ranges so thatit becomes possible to securely improve the face pressurecharacteristics and the sealing property. In the case where thecrystallization rate of the portion on the first face side exceeds 1% byweight or in the case where the crystallization rate of the portion onthe second face side becomes less than 1% by weight, the differencebetween the crystallization rates of the two sides becomes too small,failing to provide the target characteristics. In contrast, when thecrystallization rate on the second face side exceeds 10% by weight, theheat resistance on the corresponding portion may be degradated.

In accordance with the invention according to the second group of thepresent invention, since the ceramic body is composed of a catalystcarrier, and since the holding seal material is used as a catalystconverter-use holding seal material, it becomes possible to provide acatalyst-converter-use holding seal material that is also excellent inthe sealing property in addition to the advantages that it has highinitial face pressure, and is less susceptible to degradation with timein the face pressure.

In other words, in accordance with the invention according to the secondgroup of the present invention, the holding seal material is provided asa catalyst converter-use holding seal material that uses alumina-silicabased fibers as its constituent elements, and is placed in a gap betweenthe catalyst carrier and the metal shell covering the outercircumference of the catalyst carrier.

In accordance with the invention according to the second group of thepresent invention, the crystallization rate is not even, and set to bedifferent depending on portions. With this arrangement, the portion thathas a relatively high crystallization rate, and is excellent in the heatresistance is placed on a high-temperature side, and the portion thathas a relatively low crystallization rate, and is excellent in theelasticity and flexibility is placed on a low-temperature side.Therefore, the fibers are made less susceptible to brittleness on thehigh-temperature side, and on the low-temperature side, it becomespossible to avoid the occurrence of a gap to the other members. Thus, itbecomes possible to achieve a holding seal material that has anexcellent sealing property, in addition to the advantages that it hashigh initial face pressure, and is less susceptible to degradation withtime in the face pressure.

In accordance with the invention according to the second group of thepresent invention, since the ceramic body comprises a catalyst carrier,and since the holding seal material is used as a catalyst converter-useholding seal material, it becomes possible to obtain acatalyst-converter-use holding seal material that has an excellentsealing property in addition to the advantages that it has high initialface pressure, and is less susceptible to degradation with time in theface pressure.

In other words, in accordance with the invention of the second group ofthe present invention, the holding seal material is provided as acatalyst-converter-use holding seal material that includesalumina-silica based fibers as its constituent elements, and is placedin a gap between the catalyst carrier and the metal shell that coversthe outer circumference of the catalyst carrier.

In accordance with the invention according to the second group of thepresent invention, a mat-shaped fiber aggregation is sintered in amanner in which a gap is provided between the firing temperature on thefirst face side and the firing temperature on the second face side sothat it is possible to securely form a holding seal material havingdifferent crystallization rates on the respective sides comparativelyeasily. Moreover, this manufacturing method is also suitable for themanufacturing process of the holding seal material in which thecrystallization rate is gradually increased from the first face sidetoward the second face side in a sheet of fiber aggregation. Moreover, aconventional firing device is commonly applied to this manufacturingmethod without the necessity of utilizing a special firing device. Thus,it becomes possible to avoid an increase in the facility costs.

In accordance with the invention according to the second group of thepresent invention, the difference between the firing temperatures is setto 100° C. or more so that the first face side and the second face sideare made different from each other in the easiness in firing with adifference in the crystallization rates being formed between the bothfaces. Thus, it becomes possible to more securely form a holding sealmaterial having different crystallization rates on the respective sides.

In accordance with the invention according to the second group of thepresent invention, the firing temperature on the first face side is setto a temperature lower than that on the second face side; therefore,upon firing, it is possible to provide a holding seal material in whichthe crystallization rate gradually increases from the first face sidetoward the second face side.

When the firing temperature on the first face side is less than 800° C.,the firing reaction does not progress sufficiently, failing to providemechanical strength that is required. When the firing temperature on thefirst face side exceeds 1100° C. or when the firing temperature on thesecond face side is less than 1100° C., the difference between thecrystallization rates of the two sides becomes too small, failing toobtain the target characteristics. When the firing temperature on thesecond face side exceeds 1400° C., the crystallization progressesexcessively, may cause degradation in the mechanical strength and heatresistance.

The operations of the invention according to the second group of thepresent invention are described as follows. Normally, when a catalystconverter is used, the catalyst carrier, which is directly exposed to ahigh-temperature fluid, comes to have a higher temperature, while themetal shell does not have a temperature as high as the catalyst carrier.Therefore, the high-temperature resistance is especially required on theface side that is made in contact with the catalyst carrier. By takingthis fact into consideration, the above-mentioned invention allows thesecond face side that has a comparatively greater crystallization rate,that is, the face side that is excellent in the heat resistance, tocontact the catalyst carrier. Further, the first face side that has acomparatively smaller crystallization rate, that is, the face side thatis excellent in the elasticity and flexibility although it is inferiorin the heat resistance, is made in contact with the metal shell.Consequently, the fibers on the portion that is made in contact with thecatalyst carrier are less susceptible to brittleness, and make itpossible to form a holding seal material that has a high initial facepressure, and is less susceptible to degradation with time in the facepressure. Moreover, since an elastic force is exerted on the portion incontact with the metal shell, this structure makes it possible to reducethe occurrence of a gap to the metal shell, and consequently to providea holding seal material that is excellent in the sealing property.

As described above, it is possible to achieve a catalyst converter thatis excellent in the holding property in the catalyst carrier, and lesssusceptible to leakage of fluid with high process efficiency.

The following description will be given of “operations” of the thirdgroup of the present invention.

In accordance with the invention according to the third group of thepresent invention, the fiber having a non-circular shape in itscross-section becomes more flexible than the fiber having a circularshape in its cross-section. In other words, the non-circular shape ofthe above-mentioned fiber provides a characteristic in which it is bentin a specific direction comparatively easily.

Further, this characteristic makes the fiber less susceptible tobreaking, and also makes it possible to maintain the repulsive force fora long time. Here, in the present specification, “the cross-section of afiber” refers to a cross-section formed when a fiber is cutperpendicularly to the extending direction of the fiber.

In accordance with the invention according to the third group of thepresent invention, the fiber having a deformed shape in itscross-section becomes more flexible than the fiber having a circularshape in its cross-section. In other words, the deformed shape of theabove-mentioned fiber provides a characteristic in which it is bent in aspecific direction comparatively easily. Consequently, thischaracteristic makes the fiber less susceptible to breaking, and alsomakes it possible to maintain the repulsive force for a long time.

In accordance with the invention according to the third group of thepresent invention, the fiber having a flat shape in its cross-sectionbecomes more flexible than the fiber having a circular shape in itscross-section. In other words, the flat shape of the above-mentionedfiber provides a characteristic in which it is bent in a specificdirection comparatively easily. Consequently, this characteristic makesthe fiber less susceptible to breaking, and also makes it possible tomaintain the repulsive force for a long time.

In accordance with the invention according to the third group of thepresent invention, when the holding seal material is formed by usingfibers, each having a virtually elliptical or cocoon shape in itscross-section, the fibers are easily engaged with each other, making thefibers less susceptible to sliding and deviation with each other.Therefore, it becomes possible to reduce degradation in the facepressure.

In accordance with the invention according to the third group of thepresent invention, the hollow fiber having a space inside thereof isexcellent in its heat-insulating property in comparison with a fiberwithout a space inside thereof. Therefore, when the fibers of this typeare used in a holding seal material, it is possible to reduce thequantity of heat that is released from the ceramic body to the metalshell, and consequently to carry out a catalyst reaction effectively.Moreover, in the hollow fiber, sound and vibration are absorbed anddamped by the space inside the fiber. Therefore, when the fibers of thistype are used in a holding seal material, it is possible to provideexcellent noise-insulation and vibration-insulation properties.

In accordance with the invention according to the third group of thepresent invention, since the ceramic body comprises a catalyst carrier,and since the holding seal material is used as a catalyst converter-useholding seal material, it is possible to obtain a catalyst-converter-useholding seal material that is able to maintain the repulsive force for along time.

In other words, in accordance with the invention according to the thirdgroup of the present invention, the holding seal material of the presentinvention of the third group is provided as a catalyst-converter-useholding seal material that has alumina-silica based fibers as itsconstituent elements and is placed in a gap between the catalyst carrierand the metal shell covering the outer circumference of the catalystcarrier.

In accordance with the invention according to the third group of thepresent invention, a spinning stock solution is discharged through anozzle having a non-circular shape in its cross-section. Immediatelyafter discharged from the discharging section of the nozzle, theprecursor fiber has a cross-sectional shape to which the cross-sectionalshape of the discharging section is reflected in a certain degree.However, as time has elapsed since the discharge, the cross-sectionalshape thereof tends to have a roundness (in other words, is subjected tothe Barus' effect) due to the influence of a surface tension exerted onthe precursor fiber so that the cross-section of the precursor fiber hasa circular shape. Therefore, dry hot air is blown thereto in a stateimmediately after the discharge so that the precursor fiber is dried andsolidified by being removed its moisture in the precursor fiber.Consequently, it is possible to maintain a desired cross-sectional shapegiven by the discharging section of the nozzle, and consequently toobtain a fiber having a section of a non-circular shape comparativelyeasily.

In accordance with the invention according to the third group of thepresent invention, the dry hot air is blown to the precursor fiber in aforward direction with respect to the discharging direction thereof sothat the fiber is dried and solidified, and also extendedsimultaneously. Moreover, by carrying out the extending process in thismanner, it becomes possible to control the fiber diameter and shapecomparatively easily.

In accordance with the invention according to the third group of thepresent invention, a water-soluble plasticizer is preliminarily added tothe spinning stock solution so that the elastic modulus of the spinningstock solution becomes smaller with the Barus' effect being reduced.Therefore, the discharge behavior of the spinning stock solution at thetime of the spinning process is stabilized. Consequently, the fiberbecomes less susceptible to thread breakage even when it is extendedwith a strong tension, and the fiber cross-sectional shape becomes lesssusceptible to have roundness due to elastic deformation. Moreover, theabove-mentioned plasticizer has a water-soluble property so that it isdispersed in the spinning stock solution evenly. Thus, it becomespossible to reduce the Barus' ratio to a virtually fixed value, andconsequently to obtain a fiber having the target fiber diameter andcross-sectional shape comparatively easily.

The following description will be given of “operations” of the fourthgroup of the present invention.

In accordance with the invention according to the fourth group of thepresent invention, in the case where a holding seal material constitutedby alumina-silica based fibers each having a fiber diameter with thedispersions thereof being set within ±3 μm, it becomes possible toaccumulate the fibers evenly, and consequently to reduce the positionaldependence of the basis weight. Therefore, it becomes possible to reducedispersions in the face pressure value, and consequently to providestable quality.

In accordance with the invention according to the fourth group of thepresent invention, in the case where a holding seal material constitutedby alumina-silica based fibers each having a fiber length with thedispersions thereof being set within ±4 mm, it becomes possible toaccumulate the fibers evenly, and consequently to reduce the positionaldependence of the basis weight. Therefore, it becomes possible to reducedispersions in the face pressure value, and consequently to providestable quality.

In accordance with the invention according to the fourth group of thepresent invention, the synergistic effect obtained by reducing both ofthe fiber-diameter dispersion and the fiber-length dispersion makes itpossible to further reduce the positional dependence of the basisweight, and consequently to further reduce the dispersions in the facepressure value.

In accordance with the invention according to the fourth group of thepresent invention, the content of shot (non-fiber material) in theholding seal material is set to 3% by weight or less so that it becomespossible to further reduce the positional dependence of the basisweight, and consequently to further reduce the dispersions in the facepressure value.

In accordance with the invention according to the fourth group of thepresent invention, it becomes possible to extremely reduce thepositional dependence of the basis weight, and consequently to furtherreduce the dispersions in the face pressure value, and it also becomespossible to improve the face pressure and sealing property.

The average fiber diameter of less than 5 μm makes it difficult toprovide a sufficient face pressure due to a reduction in the strength ofthe fiber, and also causes a problem in which the fibers tend to beinhaled by the respiratory organs. In the case of the average fiberdiameter exceeding 15 μm, when the fibers are formed into a mat-shapedfiber aggregation, its aeration resistance is reduced, resulting indegradation in the sealing property. In addition to this adverse effect,there might be degradation in the breaking strength. This adverse effectis considered to be caused by an increase in small scratches generatedby an increase in the fiber surface area.

The case where the average fiber length being less than 5 mm causes aproblem in which the fibers tend to be inhaled by the respiratoryorgans. Moreover, this fiber no longer substantially exhibitscharacteristics as the fiber, and when the fibers are formed into amat-shaped fiber aggregation, the fibers are not allowed to entanglewith one another preferably, making it difficult to obtain a sufficientface pressure. The average fiber length exceeding 20 mm makes the fibersentangled with one another too strongly, with the result that the fiberstend to be accumulated unevenly when the fibers are formed into amat-shaped aggregation. In other words, the positional dependence of thebasis weight becomes higher, causing an adverse effect to the reductionin the dispersions in the face pressure value.

When the content of the shot is high, the positional dependence of thebasis weight becomes higher, causing an adverse effect to the reductionin the dispersions in the face pressure value.

In accordance with the invention according to the fourth group of thepresent invention, since the ceramic body is composed of a catalystcarrier, and since the holding seal material is used as a catalystconverter-use holding seal material, it becomes possible to reduce thedispersions in the face pressure value, and also to provide acatalyst-converter-use holding seal material with stable quality.

In other words, in accordance with the invention according to the fourthgroup of the present invention, the holding seal material of the fourthgroup of the present invention forms a catalyst-converter-use holdingseal material that includes alumina-silica based fibers as itsconstituent elements, and is placed in a gap between the catalystcarrier and the metal shell that covers the outer circumference of thecatalyst carrier.

In accordance with the invention according to the fourth group of thepresent invention, since the spinning process is carried out by using aninorganic salt method, it is possible to control the fiber diameter in anarrow range by properly setting the shape and size of the dischargingsection. Thus, it becomes possible to reduce dispersions in the fiberdiameter. Moreover, this method chops long fibers to obtain shortfibers; therefore, different from a method in which fibers are obtainedthrough a blowing process, it is possible to control the fiber length ina narrow range. Thus, it becomes possible to reduce dispersions in thefiber length. In addition to these effects, it is also possible to avoidthe generation of shot. Consequently, this manufacturing method makes itpossible to obtain the above-mentioned holding seal material securelywith ease.

The following description will be given of “operations” of the fifthgroup of the present invention.

In accordance with the invention according to the fifth group of thepresent invention, it is possible to provide a structure wherein, so tospeak, a cross-linking bridge is placed between portions at whichceramic fibers are adjacent to each other with overlapped parts, andconsequently to make the respective fibers less susceptible to slidingand deviation. Therefore, even when an external compressing load hasbeen imposed on the holding seal material for a long time, the member isless susceptible to reduction in the face pressure. Moreover, in theholding seal material of the present invention, the fibers are partiallybonded to each other so that the voids inside the holding seal materialare not entirely filled, thereby making it possible to maintain physicalcharacteristics (elasticity, heat insulating property and the like)originally required for the holding seal material. Moreover, since aceramic adhesive that is excellent in heat resistance is used, thebonded portions are less susceptible to reduction in the strength evenif the holding seal material is subjected to a high temperature when itis used.

In accordance with the invention according to the fifth group of thepresent invention, since the ceramic adhesive is made of a substanceconstituting the ceramic fibers, it has a high affinity for the fibers,and allows the bonded portions to have high strength.

Therefore, it becomes possible to securely prevent degradation with timein the face pressure.

In accordance with the invention according to the fifth group of thepresent invention, since alumina-silica based fibers containing a minuteamount of amorphous component are used, it is possible to improve theheat resistance of the fibers itself, and consequently to reduce thedegradation with time in the face pressure at high temperatures. Sincethe ceramic adhesive mainly composed of alumina has a very high affinityfor alumina-silica based fibers, it is possible to further providehigher strength to the bonded portions.

In accordance with the invention according to the fifth group of thepresent invention, by setting the content of the ceramic adhesive in theabove-mentioned desired range, it is possible to provide high strengthto the bonded portions while maintaining desired physical properties inthe holding seal material.

When the above-mentioned content is less than 1% by weight, the fibersmight not be bonded to one another with high strength. In contrast, inthe case where the above-mentioned content exceeds 8% by weight,although the problem with the bonding strength is solved, the voidsinside the holding seal material tend to be filled, failing to providedesired physical properties as the holding seal material.

In accordance with the invention according to the fifth group of thepresent invention, since the ceramic body is composed of a catalystcarrier, and since the holding seal material is used as a catalystconverter-use holding seal material, it is possible to provide acatalyst converter-use holding seal material which is less susceptibleto degradation with time in the face pressure even when an external loadis imposed thereon for a long time, and is also less susceptible toreduction in the strength of the bonded portions even when it issubjected to a high temperature.

In other words, in accordance with the invention according to the fifthgroup of the present invention, the holding seal material of the fifthgroup of the present invention forms a catalyst-converter-use holdingseal material that includes alumina-silica based fibers as itsconstituent elements, and is placed in a gap between the catalystcarrier and the metal shell that covers the outer circumference of thecatalyst carrier.

In accordance with the invention according to the fifth group of thepresent invention, since the firing step and the bonding process of theprecursor fibers are carried out separately, it becomes possible tosecurely obtain ceramic fibers having a desired shape in comparison witha case in which both of the processes are carried out simultaneously,and it is also possible to securely bond the fibers having theabove-mentioned desired shape. Therefore, it becomes possible tosecurely produce a holding seal material that is less susceptible todegradation with time in the face pressure with ease.

In accordance with the invention according to the fifth group of thepresent invention, since a surface tension is exerted on a materialsolution of the liquid-state ceramic adhesive, the material solution isallowed to securely adhere to portions at which the fibers are adjacentto each other with overlapped parts, when this is supplied to theaggregation. By heating this in this state, the specific component inthe material solution adhered to the corresponding portions is formedinto ceramics, thereby providing a cross-linking structure between thefibers.

In accordance with the invention according to the fifth group of thepresent invention, a surface tension is exerted on a water-soluble metalsolution with low viscosity; therefore, when the aggregation isimpregnated with this solution, the solution is allowed to securelyadhere to portions at which the fibers are adjacent to each other withoverlapped parts. Here, the impregnation method makes it possible tosecurely inject the solution to the inside of the aggregation evenly. Inthis state, the aggregation is first dried to remove moisture to acertain degree, and then heated so that the metal component in thesolution adhered to the corresponding portions is oxidized to formceramics, thereby providing a cross-linking structure between thefibers.

In accordance with the invention in accordance with the fifth group ofthe present invention, the quantity of supply of the water-soluble metalsolution is set in the aforementioned preferable range so that itbecomes possible to increase the strength of the bonded portions whilemaintaining desired physical properties of the holding seal material.

The quantity of supply of less than 1% by weight causes an insufficientquantity of the solution to adhere to the portions at which the fibersare adjacent to each other with overlapped parts, sometimes failing tomutually bond the fibers strongly.

In contrast, the quantity of supply exceeding 10% by weight causes thevoids inside the holding seal material to be easily filled with theexcessive solution, sometimes impairing desired physical properties inthe holding seal material.

In accordance with the invention according to the fifth group of thepresent invention, it is possible to form a cross-linking structure madefrom alumina having a high affinity for the fibers between thealumina-silica based fibers. Therefore, it is possible to increase thestrength of the bonded portions, and consequently to securely preventdegradation with time in the face pressure. Moreover, the fibersobtained through the inorganic salt method have a crystal structure sothat the resulting advantage is to provide higher strength at hightemperatures, in comparison with amorphous fibers obtained through afusing method.

Consequently, it is possible to obtain a holding seal material that isless susceptible to degradation in the face pressure at hightemperatures.

In accordance with the invention according to the fifth group of thepresent invention, the precursor fibers are formed into ceramics througha firing step to provide alumina-silica based fibers. In this case,portions at which the fibers are adjacent to each other with overlappedparts are bonded through a liquid-state substance (that is, ceramicadhesive) that has been formed into ceramics. In this manner, in theeleventh invention of the fifth group of the present invention, sincethe firing step and bonding process of the precursor fibers are carriedout simultaneously, it is possible to reduce the number of heating stepsin comparison with a case in which these processes are carried outseparately. Thus, it is possible to reduce the manufacturing costs.Consequently, it becomes possible to manufacture a holding seal materialthat is less susceptible to degradation with time in the face pressureeffectively at low costs.

In accordance with the invention according to the fifth group of thepresent invention, when the aggregation is put under a high humidityenvironment with high moisture, water vapor, which has entered theinside of the aggregation, is condensed to moisture. The moisture isallowed to selectively adhere to adjacent overlapped portions of thefibers through a surface tension exerted thereon. Since the precursorfibers of the alumina-silica based fibers are water-soluble so that theadjacent overlapped portions are dissolved to a certain degree due tothe adhesion of the moisture. Then, since a liquid-state substance,generated by such dissolution, has virtually the same composition as thealumina-silica based fibers, this is actually allowed to form a ceramicadhesive later. In other words, in accordance with the above-mentionedpresent invention, the liquid-state substance, which will form a ceramicadhesive later, is securely allowed to adhere to the adjacent overlappedparts. Moreover, since the liquid-state substance basically hasvirtually the same composition as the alumina-silica based fibers, ithas a high affinity for the above-mentioned precursor fibers, and makesit possible to securely bond the fibers mutually with high strength.Consequently, it becomes possible to securely prevent degradation withtime in the face pressure.

In accordance with the invention according to the fifth group of thepresent invention, a non-aqueous liquid-state substance is atomized andsupplied so that the liquid-state substance is securely injected to theinside of the aggregation, and allowed to selectively adhere to theadjacent overlapped portions between the fibers through a function ofsurface tension. In other words, in accordance with the above-mentionedpresent invention, it is possible to allow the liquid-state substancewhich will form a ceramic adhesive later to securely adhere to theadjacent overlapped parts. Moreover, the above-mentioned liquid-statesubstance is a non-aqueous substance; therefore, even when this adheresto the precursor fibers of the alumina-silica based fibers having awater-soluble property, this does not dissolve the fibers. Therefore, itis possible to avoid a possibility that the precursor fibers aredissolved too much with the result that the strength of the fibers islowered, and it is not necessary to precisely set conditions forpreventing the over-dissolving. Consequently, it is possible tomanufacture a holding seal material comparatively easily. Moreover,since the above-mentioned liquid-state substance contains inorganicelements contained in the alumina-silica based fibers so that it exertsa high affinity for the precursor fibers, and makes it possible tosecurely bond the fibers mutually with high strength. Therefore, itbecomes possible to securely prevent degradation with time in the facepressure.

In accordance with the invention according to the fifth group of thepresent invention, the following operations are obtained. Since theprecursor fibers are un-sintered and comparatively soft, these are notsusceptible to cracks and the like in a cutting portion even when animpact is exerted thereon during a cutting process. Therefore, thealumina-silica based fibers, obtained by sintering these, are excellentin mechanical strength with stable end shapes. Thus, it becomes possibleto improve the initial face pressure. In contrast, in the case where theprecursor fibers are subjected to a cutting process after having beensintered, the impact at the time of the cutting process tends to causecracks in the cutting portion of the alumina-silica based fibers. Thisis because, in general, when precursor fibers are sintered to formceramics, the fibers become brittle although they become hard.Consequently, not only the alumina-silica based fibers come to haveunstable end shapes, but also the mechanical strength of the fibers islowered.

In accordance with the invention according to the fifth group of thepresent invention, the ceramic fibers, which are aggregatedthree-dimensionally, are partially bonded to one another by a ceramicadhesive so that this structure is less susceptible to sliding anddeviation among the mutual fibers, and also less susceptible toreduction in the face pressure. Moreover, since the fibers are partiallybonded to one another in the above-mentioned ceramic fiber aggregation,the voids inside thereof are not entirely filled, with sufficientelasticity and heat-insulating property being maintained. Moreover,since the ceramic adhesive that is excellent in heat resistance is used,this structure is less susceptible to reduction in the strength in thebonded portions even when it is subjected to a high temperature.

In accordance with the invention according to the fifth group of thepresent invention, since this arrangement contains ceramic fibers havinga branching structure, it makes the fibers less susceptible to slidingand deviation with each other in comparison with an arrangement havingno branching structure.

In accordance with the invention according to the fifth group of thepresent invention, when comparison is made between an arrangement whichcontains the ceramic fibers having a branching structure and anarrangement which contain the ceramic fibers having no branchingstructure, the former is less susceptible to sliding and deviation amongthe fibers in comparison with the latter, when these are aggregatedthree-dimensionally. Thus, the former arrangement makes it possible toprovide a fiber aggregation that is less susceptible to degradation inthe face pressure.

The following description will be given of “operations” of the sixthgroup of the present invention.

The sixth group of the present invention has an arrangement in which afiring step is carried out after a spinning process, a chopping processand a mat-forming process have been executed; therefore, the cut face ofthe short fiber precursor is free from the generation of chips, burs andmicro-cracks, and this is then subjected to the firing step so that itis possible to manufacture alumina short fibers that are excellent inthe mechanical strength, and consequently to provide an alumina fiberaggregation that has a sufficiently high initial face pressure, and isless susceptible to degradation with time in the face pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a holding seal material in anembodiment of the present invention.

FIG. 2 is a perspective view for describing manufacturing processes of acatalyst converter in the above-mentioned embodiment.

FIG. 3 is a cross-sectional view showing the catalyst converter of theabove-mentioned embodiment.

FIG. 4 is a cross-sectional view showing a catalyst converter of anotherembodiment.

FIG. 5 is a schematic view for describing a firing step of a mat-shapedfiber aggregation in embodiments according to a second group of thepresent invention.

FIG. 6 is a graph showing degradation with time of face pressure inexamples and comparative examples according to the second group of thepresent invention.

FIG. 7 is a cross-sectional view showing a catalyst converter of anotherexample according to the second group of the present invention.

FIG. 8 is a schematic view showing a spinning device of an embodimentaccording to a third group of the present invention.

FIG. 9 is a schematic view showing a nozzle metal mouth shape and thecross-section of a fiber obtained through the nozzle in the examples andcomparative examples according to the third group of the presentinvention.

FIG. 10 is an SEM photograph showing a cross-section of analumina-silica based fiber 6 of example 5 according to the third groupof the present invention.

FIG. 11 is an SEM photograph showing a cross-section of analumina-silica based fiber 6 of example 7 according to the third groupof the present invention.

FIG. 12 is an enlarged cross-sectional view of a main part of a ceramicfiber of an embodiment according to a fifth group of the presentinvention.

FIG. 13 is a graph showing the results of comparison tests carried outon examples and comparative examples according to the fifth group of thepresent invention.

FIG. 14 is an SEM photograph showing ceramic fibers forming a holdingseal material according to the fifth group of the present invention.

FIG. 15( a) is an SEM photograph showing a cut face of an alumina shortfiber which is used in an alumina fiber aggregation manufactured througha manufacturing method of alumina fiber aggregation according to a sixthgroup of the present invention, and FIG. 15( b) is an SEM photographshowing a cut face of an alumina short fiber which is used in an aluminafiber aggregation manufactured through a conventional method.

FIG. 16 is a perspective view schematically showing one example of ahoneycomb filter.

FIG. 17( a) is a perspective view schematically showing one example of aporous ceramic member forming the honeycomb filter shown in FIG. 16, andFIG. 17( b) is a cross-sectional view taken along line A-A thereof.

FIG. 18 is a plan view schematically showing one example of a holdingseal material.

EXPLANATION OF SYMBOLS

-   1 catalyst converter-   2 catalyst carrier-   3 metal shell-   4 holding seal material-   6 alumina-silica based fiber-   6A precursor fiber-   7 ceramic adhesive-   17 flow path-   18 spinning stock solution-   19 nozzle-   19 a metal mouth serving as nozzle discharging section-   20 catalyst carrier-   30 honeycomb filter-   33 seal material layer-   34 bonding layer-   35 ceramic block-   40 porous ceramic member-   41 filler-   42 through hole-   43 partition wall-   50 holding seal material-   51 base material portion-   52 convex fitting section-   53 concave fitting section-   A1 extending direction-   M1 fiber aggregation-   S1 first face side-   S2 second face side

DETAILED DISCLOSURE OF THE INVENTION

First, the following description will be given of embodiments accordingto a first group of the present invention.

Referring to FIGS. 1 to 3, the following description will be given of acatalyst converter used for an automobile exhaust gas purifying deviceaccording to one embodiment of the first group of the present inventionin detail.

This catalyst converter 1 according to the embodiment of the first groupof the present invention, shown in FIG. 3, is placed in the middle of anexhaust pipe of an engine in a chassis of an automobile. Since thedistance from the engine to the catalyst converter 1 is relativelyshort, exhaust gas having a high temperature of approximately 700 to900° C. is supplied to the catalyst converter 1. In the case where theengine is a lean-burn engine, exhaust gas having a higher temperature ofapproximately 900 to 1000° C. is supplied to the catalyst converter 1.

As shown in FIG. 3, the catalyst converter 1 of the embodiment accordingto the first group of the present invention is basically constituted bya catalyst carrier 2, a metal shell 3 covering the outer circumferenceof the catalyst carrier 2, and a holding seal material 4 which is placedin a gap between the two members 2 and 3.

The catalyst carrier 2 is made from a ceramic material which istypically represented by cordierite and the like. The catalyst carrier 2is a column-shaped member having a circular shape in its cross-section.

Moreover, the cross-sectional shape of the catalyst carrier 2 is notlimited to a complete round shape, and may have, for example, anelliptical shape or an elongated circular shape. In this case, thecross-sectional shape of the metal shell 3 may be changed to anelliptical shape or an elongated circular shape correspondingly.

Moreover, the catalyst carrier 2 is preferably a honeycomb structuralbody having a number of cells 5 that extend in the axis direction. Anoble metal based catalyst such as platinum and rhodium, which canpurify exhaust gas components, is carried on the cell walls. Here, withrespect to the catalyst carrier 2, in addition to the above-mentionedcordierite carrier, for example, a honeycomb porous sintered body andthe like made of, for example, silicon carbide, silicon nitride and thelike, may be used.

Moreover, with respect to the catalyst carrier 2, in addition to thecordierite carrier molded into a honeycomb shape shown in theembodiment, a honeycomb porous sintered body made of, for example,silicon carbide, silicon nitride and the like, may be used.

In FIG. 3, the catalyst carrier 2 has a structure in which either theinlet side or the outlet side of each cell 5 is sealed with a sealingmember; however, as shown in FIG. 4, a catalyst carrier 20 having astructure in which neither the inlet side nor the outlet side of eachcell 5 is sealed with a sealing member may be used.

Here, in the following, description will be given of the catalystconverter 1 shown in FIG. 3.

With respect to the metal shell 3, in the case where, for example, apress-fitting scheme is adopted upon assembling, a metal cylinder memberhaving an O-letter shape in its cross-section is used. Here, withrespect to a metal material forming the cylinder member, metal, which isexcellent in heat resistance and impact resistance, (for example, steelproducts and the like, such as stainless steel), is preferably selected.In the case where a so-called canning scheme is adopted instead of thepress-fitting scheme, members formed by dividing the above-mentionedmetal cylinder member having the O-letter shape in its cross-sectioninto a plurality of pieces along the axis direction (that is, clamshells) are used.

In addition to this arrangement, in the case where a wrap-tighteningscheme is adopted upon assembling, for example, a metal cylinder memberhaving a C-letter shape or a U-letter shape in its cross-section, thatis, a metal cylinder member having a slit (opening section) extendingalong the so-called axis direction at only one portion, is used. In thiscase, upon assembling the catalyst carrier 2, a structure in which theholding seal material 4 is secured to the catalyst carrier 2 is housedinside the metal shell 3, and in this state, the metal shell 3 iswrapped and tightened, and the opening ends thereof is then joined (bywelding, bonding, bolt-fastening and the like). Joining works such aswelding, bonding and bolt-fastening are carried out in the same manner,also in the case where the canning scheme is adopted.

As shown in FIG. 1, the holding seal material 4 is a mat-shaped memberhaving an elongated shape, and a convex fitting section 11 is placed onits one end, and a concave fitting section 12 is placed on the otherend. As shown in FIG. 2, upon wrapping onto the catalyst carrier 2, theconvex fitting section 11 is just engaged with the concave fittingsection 12.

Moreover, the shape of the holding seal material 4 may be desirablymodified. For example, by omitting the concave and convex fittingsections 11, 12, a simpler shape may be used.

The holding seal material 4 of the embodiment according to the firstgroup of the present invention is constituted by ceramic fibersaggregated into a mat shape (that is, a fiber aggregation) serving as amain element. With respect to the above-mentioned ceramic fibers, in theembodiment according to the first group of the present invention,alumina-silica based fibers 6 are used. In this case, alumina-silicabased fibers 6 in which the mullite crystal content is set in a range of0% by weight or more to 10% by weight or less are preferably used. Sucha chemical composition makes it possible to reduce the amorphouscomponent, and consequently to provide excellent heat resistance; thus,it becomes possible to provide a high repulsive force upon applicationof a compressive load. Therefore, even when these fibers are subjectedto a high temperature while being placed in the gap, it is possible tomake them less susceptible to reduction in the face pressure.

The quantity of alumina in the alumina-silica based fibers 6 ispreferably set in a range of 40 to 100% by weight, and the quantity ofsilica is preferably set in a range of 0 to 60% by weight.

Moreover, the lower limit of the average fiber diameter of thealumina-silica based fibers 6 is set to approximately 3 μm, and theupper limit thereof is set to approximately 25 μm, more preferably, thelower limit of the average fiber diameter thereof is set toapproximately 5 μm, and the upper limit thereof is set to approximately15 μm. This is because, when the average fiber diameter is too small,the fibers tend to cause a problem in which the fibers are inhaled bythe respiratory organs. The lower limit of the average fiber length ofthe alumina-silica based fibers 6 is set to approximately 0.1 mm, andthe upper limit thereof is set to approximately 100 mm, and morepreferably, the lower limit of the average fiber length thereof is setto approximately 2 mm, and the upper limit thereof is set toapproximately 50 mm.

Different from normal alumina-silica based fibers that have atransparent whitish color, the alumina-silica based fibers 6 of theembodiment according to the first group of the present invention arecharacterized by a blackish color.

The alumina-silica based fibers 6 having “the blackish color” includethose having not only a black color (pitch-black) but also a grayishblack color.

Here, the alumina-silica based fibers 6 are preferably set to have abrightness of N8 or less which is specified in JIS Z 8721.

In this case, N of the brightness refers to a symbol determined asfollows. By setting an optimal brightness of black to 0 while setting anoptimal brightness of white to 10, the respective colors between thebrightness of black and the brightness of white are divided into 10 inbrightness, and indicated by symbols of N0 to N10, so as to allow thesense of brightness of colors in the same symbol to be represented bythe same rate.

In the actual measurements, each color is compared with color notescorresponding to N0 to N10. In this case, the first digit below thedecimal point is set to 0 or 5.

The blackish color in which the alumina-silica based fibers 6 arecolored is derived from carbon components contained in a spinning stocksolution.

The lower limit of the quantity of residual carbon components in thealumina-silica based fibers 6 is set to 1% by weight or more,preferably, the lower limit thereof is set to 1% by weight with theupper limit being set to 20% by weight, and more preferably, the lowerlimit thereof is set to 5% by weight with the upper limit being set to10% by weight. The quantity of residual carbon components of less than1% by weight tends to fail to improve the mechanical strengthsufficiently. In contrast, an excessive quantity of residual carboncomponents tends to cause degradation in the basic physical properties(for example, heat resistance and the like) of the alumina-silica basedfibers 6.

The quantity of carbon components can be calculated with respect to thereference sample during the manufacturing process, or by using a laserRaman spectrometer or based upon the intensity ratio, etc. of X-rays,the quantity of carbon components can be calculated.

The fiber tensile strength of the alumina-silica based fibers 6 ispreferably set to 1.2 GPa or more, more preferably 1.5 GPa or more. Thefiber bending strength thereof is preferably set to 1.0 GPa or more,more preferably 1.5 GPa or more. The breaking strength is set to 0.8MN/m^(3/2) or more, more preferably 1.3 MN/m^(3/2) or more. This isbecause increasing the values of the fiber tensile strength, fiberbending strength and breaking strength makes it possible to providealumina-silica based fibers 6 that can resist tension and bendingsufficiently, and are flexible and less susceptible to fracturing.

Additionally, the alumina-silica based fibers 6 of the embodimentaccording to the first group of the present invention contain carboncomponents in the fibers so that it is considered that crystallizationis allowed to progress in the entire alumina-silica based fibers 6,thereby increasing the tensile strength.

In addition to a complete round shape, the cross-sectional shape of thealumina-silica based fibers 6 may be set to a deformed cross-sectionalshape (such as an elliptical shape, an elongated circular shape and agenerally-triangular shape).

The lower limit of the thickness of the holding seal material 4 in thestate prior to the assembling process is preferably set to approximately1.1 times greater than a gap between the catalyst carrier 2 and themetal shell 3, more preferably approximately 1.5 times greater than thegap. Moreover, the upper limit of the thickness of the holding sealmaterial 4 is preferably set to approximately 4.0 times greater than agap between the catalyst carrier 2 and the metal shell 3, morepreferably approximately 3.0 times greater than the gap. Theabove-mentioned thickness of less than 1.1 times fails to provide a highcarrier holding property, resulting in the possibility of deviation andbacklash of the catalyst carrier 2 with respect to the metal shell 3.Since this case of course fails to provide a high sealing property,leakage of exhaust gas tends to occur from the gap portion, failing toachieve a high pollution-preventive property. Moreover, the thicknessexceeding 4.0 times makes it difficult to install the catalyst carrier 2in the metal shell 3 especially when the fitting-in scheme is adopted.Therefore, this case tends to fail to improve the assembling property.

The lower limit of GBD (bulk density) of the holding seal material 4after the assembling process is preferably set to 0.10 g/cm³, and theupper limit thereof is preferably set to 0.30 g/cm³; moreover, the lowerlimit of the above-mentioned GBD is more preferably set to 0.10 g/cm³,and the upper limit thereof is more preferably set to 0.25 g/cm³. Whenthe value of GBD is extremely small, it sometimes becomes difficult toachieve a sufficiently high initial face pressure. In contrast, when thevalue of GBD is extremely great, the quantity of alumina-silica basedfibers 6 to be used as a material increases, and tends to cause highcosts.

The initial face pressure of the holding seal material 4 in theassembled state is set to 50 kPa or more, more preferably 70 kPa ormore. This is because, when the value of the initial face pressure ishigh, it is possible to maintain a preferable holding property of thecatalyst carrier 2, even in the event of degradation with time in theface pressure.

Here, the holding seal material 4 may be subjected to a needle punchingprocess, a resin impregnation process and the like, if necessary. Theapplication of these processes makes it possible to compress the holdingseal material 4 in the thickness direction and consequently to make itthinner.

Next, description will be given of the sequence of processes formanufacturing a catalyst converter 1 according to the first group of thepresent invention.

First, an aluminum salt solution, silica sol and an organic polymer aremixed to form a spinning stock solution. In other words, the spinningstock solution is prepared through an inorganic salt method. Thealuminum salt solution, which forms a source of alumina, also serves asa component for applying viscosity to the spinning stock solution.

Here, with respect to such an aqueous solution, an aqueous solution ofbasic aluminum salt is preferably selected. The silica sol, which servesas a silica source, also serves as a component for giving high strengthto the fibers. The organic polymer, which is a component serving as afiber-drawing property applying agent to the spinning stock solution, isalso a component that serves as a carbon source for giving preferablemechanical strength to the alumina-silica based fibers 6 in theembodiment according to the first group of the present invention. Withrespect to the organic polymer, a straight chain polymer containingcarbon, such as PVA (polyvinyl alcohol), may be used. Here, with respectto the component serving as a carbon source, not limited to the straightchain polymer, any component having a comparatively low molecular weightwithout a chain structure (which is not a polymer) may be selected aslong as it contains carbon.

Next, by condensing under vacuum the resulting spinning stock solution,the spinning stock solution is prepared so as to have a concentration,temperature and viscosity suitable for the spinning process. In thiscase, the spinning stock solution, which had a concentration ofapproximately 20% by weight, is preferably condensed to approximately 30to 40% by weight. Moreover, the viscosity thereof is preferably set to10 to 2000 Poise.

Further, when the spinning stock solution thus prepared is dischargedinto air through a nozzle of a spinning device, a precursor fiber, whichhas a cross-sectional shape that is analogous to the nozzle metal mouthshape, is continuously obtained. The precursor fiber, thus subjected tothe spinning process, is successively wound up while being extended. Inthis case, for example, a dry-type pressurizing spinning method ispreferably adopted.

Moreover, carbon components contained in the precursor fibers thusobtained need not be derived from the organic polymer added thereto asthe fiber-drawing property applying agent, and may be derived from acarbon source applied thereto separately. In this case, not limited toonly the organic substance such as an organic polymer, for example, aninorganic substance such as carbon may be used.

Next, the precursor fiber is sintered through a firing step to be formedinto ceramics (crystallized) so that the precursor fiber is hardened toobtain an alumina-silica based fiber 6.

In the firing step, it is necessary to heat the precursor fiber under anenvironment which makes it difficult to carry out an oxidizing reactionon the carbon component (that is, the above-mentioned organic polymer)contained in the precursor fiber. More specifically, in the embodimentaccording to the first group of the present invention, the heating stepis carried out in a nitrogen atmosphere that is a typical inertatmosphere.

Here, the environment that makes it difficult to carry out an oxidizingreaction on the carbon component is not necessarily limited to an inertatmosphere, and includes, for example, an atmosphere having a reducedpressure. When the firing step is carried out in a reduced-pressureatmosphere, it is possible to suppress the progress of the oxidizingreaction in comparison with a case in which the firing step is carriedout in a normal-pressure atmosphere.

Moreover, the firing step may be carried out in an inert atmosphereother than nitrogen, such as argon, or may be carried out in areduced-pressure inert atmosphere.

Upon carrying out a heating step in a nitrogen atmosphere, the lowerlimit of the temperature is set to 1000° C., more preferably 1050° C.,and the upper limit of the temperature is set to 1300° C., morepreferably 1250° C.

The heating temperature of less than 1000° C. tends to cause aninsufficient sintering step of the precursor fiber, resulting indifficulty in stably providing an alumina-silica based fiber 6 havinghigh strength. In contrast, even when the heating temperature is set soas to exceed 1300° C., the alumina-silica based fiber 6 is not allowedto have high strength especially, and causes degradation in economicalefficiency.

In other words, in the manufacturing method of alumina-silica basedfibers according to the first group of the present invention, theheating step may be carried out on the precursor fibers in an inertatmosphere and/or under a reduced-pressure, in a firing step. Inaccordance with the manufacturing method of alumina-silica based fibersaccording to the first group of the present invention, it is possible tostably provide alumina-silica based fibers having excellent mechanicalstrength.

Successively, the long fibers of the alumina-silica based fibers 6obtained from the above-mentioned respective steps are chopped into apredetermined length to form shorter fibers in a certain extent.Thereafter, the short fibers are collected, untied and laminated, or afiber-dispersed solution, obtained by dispersing the short fibers inwater, is poured into a mold, and pressed and dried so that a mat-shapedfiber aggregation is obtained. Further, this fiber aggregation ispunched out into a predetermined shape to form a holding seal material 4having a blackish color.

Then, the holding seal material 4 is impregnated with an organic binder,if necessary, and the resulting holding seal material 4 may then becompressed and molded in the thickness direction. With respect to theorganic binder used in this case, polyvinyl alcohol, acrylic resin andthe like may be used, in addition to latex and the like such as acrylicrubber and nitrile rubber and the like.

Moreover, the holding seal material 4 is wrapped around the outercircumferential face of the catalyst carrier 2 and secured by theorganic tape 13. Thereafter, this is subjected to a press-fitting,canning or wrap-tightening step to complete a desired catalyst converter1.

Consequently, in accordance with the embodiment according to the firstgroup of the present invention, the following effects can be obtained.

The alumina-silica based fibers 6, used in the holding seal material 4,have a blackish color derived from carbon components, and is excellentin mechanical strength such as the fiber tensile strength, fiber bendingstrength and fracture toughness. Therefore, the application of thesefibers makes it possible to achieve a holding seal material 4 which hasa high initial face pressure, and is less susceptible to degradationwith time in the face pressure. Consequently, it becomes possible toobtain a catalyst converter 1 which is excellent in the holding propertyof the catalyst carrier 2 and sealing property.

In the case where the catalyst converter 1 is constituted by using theblackish alumina-silica based fibers 6, even if a substance having ablackish color such as soot has adhered to the holding seal material 4,a change in the external appearance of the holding seal material 4 ishardly noticeable. In other words, since the holding seal material 4originally has a blackish color, no major change occurs in color beforeand after the application. This point is advantageous in that anyimpression of “deteriorated” or “stained” is not given to the user.

In accordance with the manufacturing method of the embodiment accordingto the first group of the present invention, the firing step forsintering the precursor fibers is executed by carrying out a heatingstep under an environment which makes it difficult to carry out anoxidizing reaction on the carbon component contained in the precursorfibers. Therefore, it is possible to allow much carbon components toremain in the alumina-silica based fibers 6, and consequently tosecurely provide alumina-silica based fibers 6 that are excellent inmechanical strength with ease.

In accordance with the manufacturing method of the embodiment accordingto the first group of the present invention, an inexpensive nitrogenatmosphere is used as the inert atmosphere in which the firing step iscarried out. For this reason, it is possible to reduce manufacturingcosts of the holding seal material 4. Moreover, since the heating stepis carried out by setting the firing temperature within theabove-mentioned preferable range, it becomes possible to stably obtainalumina-silica based fibers 6 with high strength.

In accordance with the manufacturing method of the embodiment accordingto the first group of the present invention, the carbon componentcontained in the precursor fibers is derived from the organic polymerthat has been added to the spinning stock solution as a fiber-drawingproperty applying agent. Therefore, it is not necessary to especiallyadd carbon sources to the spinning stock solution in a separated manner,thereby making it possible to eliminate the necessity of greatlymodifying the composition of the spinning stock solution. Thus, it ispossible to preliminarily avoid imbalance in the stock solutioncomposition, and consequently to prevent degradation in the basicphysical properties in the alumina-silica based fibers 6. Moreover,since no carbon source needs to be added, it becomes possible to reducethe manufacturing costs. Furthermore, since the above-mentioned organicpolymer is easily dispersed in the spinning stock solution evenly, thecarbon sources are evenly dispersed in the precursor fibers.Consequently, the resulting alumina-silica based fibers 6 are allowed tohave an even residual carbon content, and less susceptible toirregularity in the mechanical strength.

Moreover, the embodiment according to the first group of the presentinvention has exemplified a case where the holding seal material 4according to the first group of the present invention is applied to acatalyst converter 1 used for an exhaust gas purifying device; however,the holding seal material 4 according to the first group of the presentinvention may of course be applied to devices other than the catalystconverter 1 used for an exhaust gas purifying device, such as a dieselparticulate filter (DPF), a catalyst converter used for a fuel cellmodifier and the like.

The following description will be given of an embodiment according to asecond group of the present invention.

Referring to FIGS. 1 to 6, the following description will be given of acatalyst converter used for an automobile exhaust gas purifying devicein accordance with one embodiment of the second group of the presentinvention in detail.

This catalyst converter 1 according to the embodiment of the secondgroup of the present invention, shown in FIG. 3, is substantially thesame as the catalyst converter according to the first group of thepresent invention, and formed from a catalyst carrier 2, a metal shell 3covering the outer circumference of the catalyst carrier 2, and aholding seal material 4 which is placed in a gap between the two members2 and 3.

Moreover, in the same manner as a catalyst converter 1 of anotherexample shown in FIG. 7, this converter may have a structure in which:the holding seal material 4 is constituted by a plurality of sheets (twoin this case) of fiber aggregations M1 having mutually differentcrystallization rates, and these fiber aggregations M1 may be superposedand bonded to each other. In this case, the fiber aggregation M1 havinga smaller crystallization rate needs to be made in contact with themetal shell 3, and the fiber aggregation M1 having a greatercrystallization rate needs to be made in contact with the catalystcarrier 2.

Here, with respect to the catalyst carrier 2 and the metal shell 3, thesame members that have been explained in the catalyst converteraccording to the first group of the present invention may be used;therefore, the description thereof is omitted.

Moreover, not limited to a complete round shape, the cross-sectionalshape of the catalyst carrier 2 may be set to, for example, anelliptical shape or an elongated circular shape. In such a case, thecross-sectional shape of the metal shell 3 may be modified to anelliptical shape or an elongated circular shape in a correspondingmanner.

Moreover, with respect to the catalyst carrier 2, in addition to acordierite carrier molded into a honeycomb shape shown in theembodiment, for example, a honey comb porous sintered body of, forexample, silicon carbide or silicon nitride and the like, may be used.

Furthermore, as shown in the catalyst carrier 20 shown in FIG. 4, thosehaving no sealing member may be used.

As shown in FIG. 1, the holding seal material 4 is a mat-shaped memberhaving an elongated shape, and a convex fitting section 11 is placed onits one end, and a concave fitting section 12 is placed on the otherend. As shown in FIG. 2, upon wrapping onto the catalyst carrier 2, theconvex fitting section 11 is just engaged by the concave fitting section12.

Moreover, the shape of the holding seal material 4 may be desirablymodified. For example, by omitting the recessed and convex fittingsections 11, 12, a simpler shape may be used.

The holding seal material 4 in accordance with the embodiment accordingto the second group of the present invention is constituted by ceramicfibers aggregated into a mat shape (that is, a fiber aggregation M1)serving as a main element. With respect to the above-mentioned ceramicfibers, in the embodiment according to the second group of the presentinvention, alumina-silica based fibers 6 are used.

In the holding seal material 4 of the embodiment according to the secondgroup of the present invention, the mullite crystallization rate is noteven, but different depending on portions thereof. In other words, inone sheet of fiber aggregation M1, the crystallization rate on the firstface side S1 portion and the crystallization rate on the second faceside S2 portion are different from each other, and more specifically,the crystallization rate is allowed to gradually increase from the firstface side S1 toward the second face side S2.

Here, the first face side S1 in the holding seal material 4 is a faceside that is subjected to a firing step at a comparatively lowtemperature, and is placed in a manner so as to contact the metal shell3 side on which heat resistance is not required so much. Therefore, thefirst face side S1 may be regarded as a low-temperature firing face or ashell-side contact face. The second face side S2 is a face side that issubjected to a firing step at a comparatively high temperature, and isplaced in a manner so as to contact the catalyst carrier 2 side on whichheat resistance is required. Therefore, the second face side S2 may beregarded as a high-temperature firing face or a bearing-member sidecontact face.

In this case, the difference between the crystallization rate of thesurface layer portion of the first face side S1 and the crystallizationrate of the surface layer portion of the second face side S2 ispreferably set to 3% by weight or more. More specifically, thecrystallization rate of the surface layer portion of the first face sideS1 is preferably set to 0 to 1% by weight, and the crystallization rateof the surface layer portion of the second face side S2 is preferablyset to 1 to 10% by weight.

In the case where the crystallization rate of the surface layer portionon the first face side S1 exceeds 1% by weight and in the case where thecrystallization rate of the surface layer portion on the second faceside S2 is less than 1% by weight, the difference between thecrystallization rates of the two sides becomes too small, failing toobtain target characteristics. In the case where the crystallizationrate of the surface layer portion on the second face side S2 exceeds 10%by weight, the heat resistance of the corresponding portion might belowered. Additionally, it is preferable to set the crystallization rateof the surface layer portion on the first face side S1 to 0% by weight,that is, it is preferable to form the corresponding portion by using anamorphous material.

Here, the above-mentioned crystallization rate is measured based uponpeaks of mullite by using X-ray diffraction; and supposing that thematerial having no peak is set to 0% by weight in crystallization rate,a peak measured by 100% mullite is set to 100% by weight incrystallization rate, and the corresponding crystallization rate can bemeasured from a ratio between the value at 100% by weight and a sampledvalue.

Moreover, the above-mentioned crystallization rate may be obtained bycalculating the weight ratio from the difference between dissolvingrates of mullite and silica in an HF solution.

With respect to the quantity of alumina, the quantity of silica in thealumina-silica based fibers 6, the average fiber diameter of thealumina-silica based fibers 6 and the average fiber length, thesefactors are preferably set in the same manner as those explained in thecatalyst converter according to the first group of the presentinvention; therefore, the description thereof is omitted.

With respect to the alumina-silica based fibers 6 located on the secondface side S2, it is preferable to set the fiber tensile strength to 1.0GPa or more, the fiber bending strength to 0.8 GPa or more, and theelastic modulus to 9.5×10¹⁰ N/m² or more, respectively. With respect tothe alumina-silica based fibers 6 located on the first face side S1, itis preferable to set the fiber tensile strength to 2.0 GPa or more, thefiber bending strength to 1.5 GPa or more, and the elastic modulus to11.0×10¹⁰ N/m² or more, respectively. The reason for this is because, asthe fiber tensile strength, the fiber bending strength and the like areincreased, the alumina-silica based fibers 6 come to have very strongresistance to tensile and bending.

The cross-sectional shape of the alumina-silica based fibers 6, thethickness of the holding seal material 4 prior to the assemblingprocess, the GBD (bulk density) of the holding seal material 4 after theassembling process and the initial face pressure of the holding sealmaterial 4 in the assembled state of the embodiment according to thesecond group of the present invention are preferably set in the samemanner as those described in the catalyst converter according to thefirst group of the present invention; therefore, the description thereofis omitted.

Here, such a holding seal material 4 may be subjected to a needlepunching process, a resin impregnation process, etc., if necessary. Byapplying these processes, it becomes possible to compress the holdingseal material 4 in the thickness direction, and consequently to make itthinner in the thickness direction.

The following description will be given of a sequence of processes formanufacturing a catalyst converter 1 according to the second group ofthe present invention.

First, a spinning stock solution is prepared in the same manner as themethod explained in the manufacturing method of the catalyst converteraccording to the first group of the present invention so that longfibers of the precursor fibers are produced.

Successively, the long fibers of the precursor fibers are chopped into apredetermined length to form shorter fibers in a certain extent.Thereafter, the short fibers are collected, untied and laminated, or afiber-dispersed solution, obtained by dispersing the short fibers inwater, is poured into a mold, and pressed and dried so that a mat-shapedfiber aggregation M1 is obtained.

Following the above-mentioned laminating process, the fiber aggregationM1 is subjected to a firing step so that the precursor fibers aresintered, and formed into ceramics (crystallized). Thus, the precursorfibers are hardened to form alumina-silica based fibers 6. FIG. 5 showsan electric furnace 21 that is used as a firing device in the embodimentaccording to the second group of the present invention.

Here, the firing step may be carried out by using a firing device otherthan the exemplified electric furnace 21.

The above-mentioned electric furnace 21 is a device for continuouslyheating and sintering an object to be fired while it is beingtransported in the horizontal direction. A net conveyor belt 23 servingas a transporting means is housed in a main body 22 constituting theelectric furnace 21. A mat-shaped fiber aggregation M1 that is an objectto be fired is placed on the net conveyor belt 23. An upper-sideelectric heater 24 serving as a first heating means is placed above thenet conveyor belt 23 with a gap therefrom, and a lower-side electricheater 25 serving as a second heating means is placed below the netconveyer belt 23 with a gap therefrom. These electric heaters 24, 25 areconnected to a power supply through a temperature-control means, whichis not shown. In this device, these two kinds of electric heaters 24 and25 are individually temperature-controlled.

In the firing step, after a preliminary heating step (preliminaryprocess) has been carried out on the above-mentioned fiber aggregationM1 in the electric furnace 21 that is maintained in an atmosphericpressure that is a normal pressure, a main heating step (firing step) iscarried out in the electric furnace 21 that is maintained also in anatmospheric pressure that is a normal pressure.

In this case, the temperature settings of these two kinds of electricheaters 24, 25 are changed so as to provide a temperature difference toa certain degree. In other words, the fiber aggregation M1 is sinteredwith a difference being set between the firing temperature on the firstface side S1 and the firing temperature on the second face side S2.Here, in the embodiment according to the second group of the presentinvention, the set temperature of the electric heater 24 on the upperside is higher than the set temperature of the electric heater 25 on thelower side.

In this case, the difference between the set temperatures at the time ofthe firing step is preferably set to 100° C. or more, especially 200° C.or more. The above-mentioned temperature difference of less than 100° C.fails to provide a sufficient difference in the easiness of sinteringbetween the first face side S1 and the second face side S2, making itdifficult to provide a difference in the crystallization rates.

Moreover, the firing temperature of the first face side S1 is preferablyset in a range of 800 to 1100° C., and the firing temperature of thesecond face side S2 is preferably set in a range of 1100 to 1400° C.

The firing temperature on the first face side S1 of less than 800° C.fails to allow the sintering reaction to progress sufficiently, failingto obtain the required mechanical strength. When the firing temperatureon the first face side S1 exceeds 1100° C., or when the firingtemperature on the second face side S2 is less than 1100° C., thedifference in the crystallization rate between the two sides becomes toosmall, failing to provide target characteristics.

The firing temperature exceeding 1400° C. on the second face side S2makes the crystallization to progress too quickly, resulting indegradation in the mechanical strength and heat resistance.

Moreover, the firing time (more specifically, the time during which themaximum heating temperature is maintained) is preferably set in a rangeof 10 to 60 minutes. If the firing time is too short, the sinteringreaction might not progress sufficiently even when the temperature isset to be sufficiently high. Consequently, it becomes impossible toobtain mechanical strength required. If the firing time is too long, theproduction efficiency is lowered, and the crystallization might progresstoo quickly, resulting in degradation in the mechanical strength andheat resistance.

In the succeeding punch-out process, the mat-shaped fiber aggregation M1that has been subjected to the firing step is punched out into apredetermined shape to form a holding seal material 4.

Then, after the holding seal material 4 has been impregnated with anorganic binder, if necessary, the holding seal material 4 may be furthercompressed, and molded in the thickness direction. With respect to theorganic binder used in this case, polyvinyl alcohol, acrylic resin andthe like may be used, in addition to latex and the like such as acrylicrubber and nitrile rubber and the like.

Further, the holding seal material 4 is wrapped around the outercircumferential face of the catalyst carrier 2 and secured by theorganic tape 13. Thereafter, this is subjected to a press-fitting,canning or wrap-tightening process to complete a desired catalystconverter 1.

Here, the exemplified holding seal material 4 has a structure, that isto say, in which its crystallization rate differs along the thicknessdirection. In contrast, the holding seal material in which itscrystallization rate differs in the length direction, or the holdingseal material in which its crystallization rate differs in the widthdirection, may be provided. For example, when the latter holding sealmaterial is wrapped around the catalyst carrier 2, the catalyst carrier2 is allowed to have different crystallization rates between its one endand the other end. In other words, the one end is allowed to haveexcellent heat resistance, while the other end is allowed to haveexcellent elasticity and flexibility. Therefore, when the end portion onthe side having a greater crystallization rate and excellent heatresistance is placed so as to face the exhaust gas flow-in side, itbecomes possible to achieve a catalyst converter 1 having excellentresistance and wind erosion resistance.

Consequently, in accordance with the embodiment according to the secondgroup of the present invention, the following effects can be obtained.

Normally, when the catalyst converter 1 is used, the catalyst carrier 2,which is directly exposed to high-temperature exhaust gas, comes to havea high temperature, while the temperature of the metal shell 3 does notbecome so high as the temperature of the catalyst carrier 2. Therefore,the face side that is made in contact with the catalyst carrier 2requires especially high temperature resistance. By taking these factsinto consideration, the embodiment according to the second group of thepresent invention has an arrangement in which the second face side S2having a relatively higher crystallization rate, that is, the face sidehaving excellent heat resistance, is made in contact with the catalystcarrier 2. In contrast, the first face side S1 having a relatively lowercrystallization rate, that is, the face side that is excellent inelasticity and flexibility although it is inferior in heat resistance,is allowed to contact the metal shell 3. Therefore, the fibers at theportion contacting the catalyst carrier 2 are less susceptible tobrittleness, making it possible to provide a holding seal material 4which has a high initial face pressure, and is less susceptible todegradation with time in the face pressure. Moreover, since an elasticforce is exerted at the portion contacting the metal shell 3, it ispossible to reduce the occurrence of a gap with the metal shell 3, andconsequently to provide a holding seal material 4 that is excellent inthe sealing property.

As described above, it is possible to achieve a catalyst converter 1that is excellent in the holding property of the catalyst carrier 2, andless susceptible to exhaust gas leakage, and has good processefficiency.

The holding seal material 4 according to the second group of the presentinvention comprises a sheet of fiber aggregation M1, and thecrystallization rate is gradually increased from the first face side S1toward the second face side S2 of the fiber aggregation M1. Therefore,different from a structure constituted by a plurality of fiberaggregations M1 having different crystallization rates, it becomespossible to eliminate the necessity of jobs for mutually superposing thefiber aggregations M1 and for bonding these to each other, andconsequently to reduce the number of manufacturing processes. Thus, itbecomes possible to provide a holding seal material 4 that is easilymanufactured.

Moreover, since it is possible to make the structure thinner incomparison with a superposed structure having a plurality of sheets, itbecomes possible to place the structure in a narrow gap comparativelywith ease. Thus, it is possible to easily carry out not only awrap-tightening process, but also a fitting-in process at the time ofthe canning operation.

Furthermore, in the superposed structure having a plurality of sheets,exhaust gas might pass through the interface between the fiberaggregations M1. In contrast, since this holding seal material 4 has asingle-sheet structure that is free from the interface, it is notnecessary to take the passage of exhaust gas into consideration. Thus,it becomes possible to provide a device having an excellent sealingproperty.

In this holding seal material 4, the crystallization rate of the portionon the first face side S1 and the crystallization rate of the portion onthe second face side S2 are set in the above-mentioned desirable range.Therefore, it is possible to securely improve the face pressurecharacteristic and sealing property, and to achieve a catalyst converter1 having high performances.

In a manufacturing method of the embodiment according to the secondgroup of the present invention, the firing step is carried out with agap being provided between the firing temperature of the first face sideS1 and the firing temperature of the second face side S2 of themat-shaped fiber aggregation M1. Therefore, it is possible to securelymanufacture a holding seal material 4 having different crystallizationrates on its surface and rear surface comparatively with ease. Moreover,such a manufacturing method is extremely suited for providing a holdingseal material 4 having an arrangement in which the crystallization rateis gradually increased from the first face side S1 toward the secondface side S2 in a single sheet of fiber aggregation M1. Furthermore, aconventional firing device is commonly applied to this manufacturingmethod without the necessity of applying a special firing device. Thus,it becomes possible to avoid an increase in the facility costs.

In the embodiment according to the second group of the presentinvention, the firing step is carried out with the firing temperatureson the first face side S1 and the second face side S2 being set withinthe above-mentioned preferable range. Therefore, it becomes possible tosecurely manufacture the holding seal material 4 of the embodimentaccording to the second group of the present invention in which thecrystallization rate gradually increases from the first face side S1toward the second face side S2.

Furthermore, the holding seal material according to the second group ofthe present invention is provided as a holding seal material thatincludes alumina-silica based fibers aggregated into a mat shape as itsconstituent elements, and is placed in a gap between the catalystcarrier and the metal shell that covers the outer circumference of thecatalyst carrier, and this holding seal material may be provided as acatalyst-converter-use holding seal material that is characterized by astructure in which the first-face-side portion is made from an amorphousmaterial and the second-face-side portion is made from a crystalmaterial.

With this arrangement, it becomes possible to achieve a holding sealmaterial for catalyst-converter-use that has an excellent sealingproperty in addition to the advantages that it has high initial facepressure, and is less susceptible to degradation with time in the facepressure.

Here, the embodiment according to the second group of the presentinvention has exemplified a case in which the holding seal material 4 isapplied to a catalyst converter 1 used for an exhaust-gas-purifyingdevice. However, the holding seal material 4 according to the secondgroup of the present invention may of course be applied to devices otherthan the catalyst converter 1 used for an exhaust-gas-purifying device,such as a diesel particulate filter (DPF) and a catalyst converter usedfor a fuel cell modifier.

The following description will be given of an embodiment according to athird group of the present invention.

Referring to FIGS. 1 to 3, as well as FIGS. 8 and 9, the followingdescription will be given of a catalyst converter used for an automobileexhaust gas purifying device in accordance with one embodiment accordingto the third group of the present invention in detail.

This catalyst converter 1 in accordance with the embodiment of the thirdgroup of the present invention, shown in FIG. 3, is virtually the sameas the catalyst converter according to the first group of the presentinvention, and constituted by a catalyst carrier 2, a metal shell 3covering the outer circumference of the catalyst carrier 2, and aholding seal material 4 that is placed in a gap between the two members2 and 3.

Here, with respect to the catalyst carrier 2 and the metal shell 3, thesame members that have been explained in the catalyst converteraccording to the first group of the present invention may be used;therefore, the description thereof is omitted.

Moreover, not limited to a complete round shape, the cross-sectionalshape of the catalyst carrier 2 may be set to, for example, anelliptical shape or an elongated circular shape.

Moreover, with respect to the catalyst carrier 2, in addition to acordierite carrier molded into a honeycomb shape shown in theembodiment, for example, a honey comb porous sintered body of, forexample, silicon carbide or silicon nitride and the like, may be used.

Furthermore, as shown in the catalyst carrier 20 shown in FIG. 4, thosehaving no sealing member may be used.

As shown in FIG. 1, the holding seal material 4 is a mat-shaped memberhaving an elongated shape, and a convex fitting section 11 is placed onits one end, and a concave fitting section 12 is placed on the otherend. As shown in FIG. 2, upon wrapping onto the catalyst carrier 2, theconvex fitting section 11 is just engaged by the concave fitting section12.

The holding seal material 4 in accordance with the embodiment accordingto the third group of the present invention is constituted by ceramicfibers aggregated into a mat shape (that is, a fiber aggregation)serving as a main element. With respect to the above-mentioned ceramicfibers, in the embodiment according to the third group of the presentinvention, alumina-silica based fibers 6 are used. In this case, thealumina-silica based fibers 6, which have a mullite crystal content in arange of 0% by weight or more to 10% by weight or less, are preferablyused. The fibers having such a chemical composition make it possible toprovide excellent heat resistance and a high repulsive force uponapplication of a compressing load, because the amorphous componentthereof becomes smaller. Therefore, even when it is subjected to a hightemperature while being placed in the gap, the possibility of reductionin the face pressure to be generated is comparatively lowered.

The chemical composition of the alumina-silica based fibers 6 ispreferably set so that alumina is in a range of 68 to 83% by weight andsilica is in a range of 32 to 17% by weight, and specifically,Al₂O₃:SiO₂=72:28 is more preferred.

If alumina is less than 68% by weight, or if silica exceeds 32% byweight, it might be difficult to improve the heat resistance and therepulsive force upon application of a compressing load sufficiently. Inthe case where alumina exceeds 83% by weight, or in the case wheresilica is less than 17% by weight also, it might be difficult to improvethe heat resistance and the repulsive force upon application of acompressing load sufficiently.

With respect to the average fiber diameter and the average fiber lengthof the alumina-silica based fibers 6, these are preferably set in thesame manner as explained in the catalyst converter according to thefirst group of the present invention; therefore, the description thereofis omitted.

Moreover, the tensile strength of each of the alumina-silica basedfibers 6 is preferably set to 0.1 GPa or more, more preferably 0.5 GPaor more.

Here, the alumina-silica based fibers 6 of the embodiment according tothe third group of the present invention needs to have a non-circularshape in the cross-section thereof, that is, a deformed shape in thecross-section thereof. Some examples of the fibers having a deformedcross-sectional shape are shown on the right-side column of a table inFIG. 9. A fiber having a virtually elliptical cross-section (fiberhaving an elliptical cross-section) is shown on the first row in theright-side column as one example of the fiber having a flatcross-sectional shape. A fiber having a cross-section with a virtuallycocoon-shape (fiber having a cocoon-shaped cross-section) is shown onthe second row in the right-side column as one example of the fiberhaving a flat cross-sectional shape. Moreover, a hollow fiber having anempty space inside thereof is shown on the third row in the right-sidecolumn.

Moreover, not limited to the exemplified elliptical shape and cocoonshape, the cross-sectional shape of the alumina-silica based fibers 6may be set to, for example, an elongated circular shape, a triangularshape or a rectangular shape.

Furthermore, not limited to the exemplified hollow shape, thecross-sectional shape of the alumina-silica based fibers 6 may be setto, for example, a shape having two or more spaces inside thereof andthe like.

In the catalyst converter according to the third group of the presentinvention, the thickness of the holding seal material 4 prior to theassembling process, the GBD (bulk density) of the holding seal material4 after the assembling process and the initial face pressure of theholding seal material 4 in the assembled state are preferably set in thesame manner as those described in the catalyst converter according tothe first group of the present invention; therefore, the descriptionthereof is omitted.

Here, the holding seal material 4 may be subjected to a needle punchingprocess, a resin impregnation process, etc., if necessary. By applyingthese processes, it becomes possible to compress the holding sealmaterial 4 in the thickness direction, and consequently to make itthinner in the thickness direction.

The following description will be given of a sequence of processes formanufacturing a catalyst converter 1 according to the third group of thepresent invention.

First, a spinning stock solution 18 is prepared by mixing an aluminumsalt aqueous solution, silica sol and an organic polymer. In otherwords, the spinning stock solution 18 is prepared by using an inorganicsalt method. The aluminum salt aqueous solution, which serves as analumina source, also serves as a component giving viscosity to thespinning stock solution 18. With respect to such an aqueous solution, anaqueous solution of basic aluminum salt is preferably selected. Thesilica sol, which serves as a silica source, also serves as a componentfor giving high strength to the fibers. The organic polymer is acomponent for giving a fiber-drawing property to the spinning stocksolution 18.

In the embodiment according to the third group of the present invention,a water-soluble plasticizer is preferably further added to the spinningstock solution 18 as a Barus'-ratio reducing agent at the time ofnozzle-discharging. The lower limit of the amount of addition of theabove-mentioned plasticizer is preferably set to 0.1% by weight with theupper limit thereof being preferably set to 10% by weight, andparticularly, the lower limit thereof is more preferably set to 0.1% byweight with the upper limit being set to 3% by weight.

When the above-mentioned amount of addition is less than 0.1% by weight,the elastic modulus is not lowered sufficiently with the result that theexpected Barus' ratio reducing effect by the addition of the plasticizermight not be obtained. In contrast, the amount of addition exceeding 10%by weight tends to cause adverse effects on the physical properties ofthe alumina-silica based fibers 6 as the ratio of non-ceramic componentsin the spinning stock solution 18 increases.

Moreover, the Barus' ratio may be reduced by using a method other thanthe method of adding a water-soluble substance to the spinning stocksolution 18.

With respect to the above-mentioned plasticizer, a water-soluble organicsubstance is preferably selected, and more specifically, glycol etherswith high viscosity may be preferably selected. The organic substancesof this type make it possible to securely reduce the elastic modulus ofthe spinning stock solution 18 even by a small amount of addition.Moreover, glycol ethers are completely burned to disappear by heat thatis applied up to the end of the sintering step carried out after thespinning process.

Here, examples of glycol ethers that can be used as the plasticizerinclude: tetraethylene glycol monobutyl ether (3,6,9,12-tetraoxahexadecanol), triethylene glycol monobutyl ether (3,6,9-trioxamidecanol),diethylene glycol monobutyl ether (2-(2-butoxyethoxy) ethanol),propylene glycol monobutyl ether, ethylene glycol monobutyl ether,propylene glycol monomethyl ether (1-methoxy-2-propanol), a mixture ofpropylene glycol monomethyl ether acetate and acetic acid and the like.Besides the above-mentioned glycol ethers, for example, a viscousorganic substance such as polyethylene glycol and glycerin and the likemay be used as the plasticizer. Moreover, only one kind of these organicsubstances listed here may be added to the spinning stock solution 18;however, two kinds or more of these may be combined and added thereto.

Next, the resulting spinning stock solution 18 is condensed under vacuumso as to provide a spinning stock solution 18 that has been adjusted tohave a density, temperature and viscosity suited for the spinningprocess. Here, the spinning stock solution 18, which has been set to aconcentration of approximately 20% by weight, is condensed andpreferably set to approximately 30 to 40% by weight. Moreover, theviscosity is preferably set to 10 to 1500 Poise.

Moreover, the spinning stock solution 18 thus prepared is dischargedinto the air through a nozzle 19 of a spinning device 20 shown in FIG. 8so that a precursor fiber 6A, which has a cross-sectional shape that isapproximated by the cross-sectional shape of a metal mouth 19 a servingas a nozzle discharging section, is continuously obtained. Morespecifically, the precursor fiber 6A, which has a fiber with anelliptical cross-section as shown on the first row in the right-sidecolumn, is produced by using a metal mouth 19 a having a rectangularcross-section shown on the first row in the right-side column. Theprecursor fiber 6A having a cocoon cross-sectional shape shown on thesecond row in the right-side column is produced by using a metal mouth19 a having a virtually dumbbell shaped cross-section shown on thesecond row in the left-side column of the table in FIG. 9. The precursorfiber 6A having a hollow cross-sectional shape shown on the third row inthe right-side column is produced by using a metal mouth 19 a having avirtually C-letter shape shown on the third row on the left-side columnof the table in FIG. 9.

Here, in the case of the fiber having an elliptical cross-sectionalshape as shown on the first row on the right side of the table in FIG.9, the degree of oblateness (ratio of a minor axis and a major axis) ispreferably set in a range of 1:1.1 to 1:3. The fiber having a degree ofoblateness exceeding 1:3 might cause a reduction in the initial facethickness.

Then, the precursor fiber 6A, thus spun out through the metal mouth 19a, is successively taken up while being extended. In this case, forexample, a dry-type pressurizing spinning method may be preferably used.

Preferably, dry hot air is blown to the precursor fiber 6A immediatelyafter it has been discharged from the metal mouth 19 a. In this case, itis preferable to blow dry hot air, and more preferable to blow hot airhaving a temperature of normal temperature or more. With thisarrangement, it becomes possible to dry the precursor fiber 6A quicklywith high efficiency.

In the case of the spinning device 20 shown in FIG. 8, a flow path 17through which dried hot air is allowed to flow is formed in the nozzle19. A dry air discharge port, which opens downward (in the samedirection as the nozzle 19) at a position just next to the metal mouth19 a of the nozzle 19, is formed on one end of the flow path 17. Theother end of the flow path 17 is connected to an air source through apipe which is not shown, not shown. Therefore, when pressurized air,which has been heated and dried, is supplied, dried hot air isdischarged in a forward direction with respect to the dischargingdirection (in other words, extending direction A1: downward direction inFIG. 8) of the precursor fiber 6A. As a result, the precursor fiber 6A,immediately after discharged, is dried by hot air. The temperature ofthe dried hot air is preferably set to 30 to 100° C., and the wind speedis preferably set to 1 to 50 m/s.

Next, the precursor fiber 6A is sintered through a firing step to beformed into ceramics (crystallized) so that the precursor fiber 6A ishardened to obtain an alumina-silica based fiber 6. Here, theplasticizer is completely burned to disappear by heat at this time, andhardly remains in the alumina-silica based fibers 6.

In the above-mentioned firing step, it is preferable to set the firingcondition so as to make the mullite crystal content in the resultingalumina-silica based fibers 6 having 10% by weight or less. For example,the firing temperature in the firing step is preferably set in a rangeof 1000 to 1300° C. The firing temperature of less than 1000° C. failsto completely dry and sinter the precursor fibers 6A, with the resultthat it becomes difficult to securely provide excellent heat resistanceand a high repulsive force at the time of application of a compressingload to the holding seal material 4. In contrast, in the case of afiring temperature exceeding 1300° C., the mullite crystallization inthe alumina-silica based fiber 6 is allowed to easily progress. For thisreason, it becomes difficult to reduce the mullite crystal content to10% by weight or less, and consequently, it may not be able to securelyprovide excellent heat resistance and a high repulsive force at the timeof application of a compressing load to the holding seal material 4.

Successively, the long fibers of the alumina-silica based fiber 6 thathave been obtained through the above-mentioned respective processes arechopped into a predetermined length to form shorter fibers in a certainextent. Thereafter, the short fibers are collected, untied andlaminated, or a fiber-dispersed solution, obtained by dispersing theshort fibers in water, is poured into a mold, and pressed and dried sothat a mat-shaped fiber aggregation is obtained. Further, this fiberaggregation is punched out into a predetermined shape to form a holdingseal material 4.

Thereafter, the holding seal material 4 is impregnated with an organicbinder, if necessary, and the resulting holding seal material 4 may thenbe compressed and molded in the thickness direction. With respect to theorganic binder used in this case, polyvinyl alcohol, acrylic resin andthe like may be used, in addition to latex and the like such as acrylicrubber and nitrile rubber and the like.

Moreover, the holding seal material 4, obtained by punching out theabove-mentioned fiber aggregation into a predetermined shape, is wrappedaround the outer circumferential face of the catalyst carrier 2 andsecured by the organic tape 13. Thereafter, this is subjected to apress-fitting, canning or wrap-tightening process to complete a desiredcatalyst converter 1.

Consequently, in accordance with the embodiment according to the thirdgroup of the present invention, the following effects can be obtained.

The holding seal material 4 of the embodiment according to the thirdgroup of the present invention is constituted by alumina-silica basedfibers 6 having a cross-section that is not a circular shape, but adeformed shape. The fibers of this type become more flexible incomparison with fibers having a circular cross-sectional shape. In otherwords, since the alumina-silica based fiber 6 has a non-circular shape,it has such a characteristic that it is bent in a specific directioncomparatively easily. This characteristic makes the alumina-silica basedfibers 6 less susceptible to breaking, and allows them to maintain therepulsive force for a long time. Thus, in case of the holding sealmaterial 4 manufactured by using such alumina-silica based fibers 6, itbecomes possible to reduce the possibility of degradation with time inthe face pressure. Therefore, it is possible to achieve a catalystconverter 1 which is excellent in the holding property of the catalystcarrier 2 and the sealing property against exhaust gas.

Moreover, in the case of the holding seal material 4 using fibers havingan elliptical cross-sectional shape and fibers having a cocoon-shapedcross-section, the alumina-silica based fibers 6 are easily engaged withone another, so that the alumina-silica based fibers 6 are lesssusceptible to sliding and deviation.

Therefore, it becomes possible to reduce degradation in the facepressure.

Moreover, the hollow fibers are excellent in heat-insulating property incomparison with those having no space inside thereof. Therefore, theholding seal material 4 using such fibers makes it possible to reducethe quantity of heat that is released from the catalyst carrier 2 to themetal shell 3, and consequently to carry out a catalyst reaction withhigh efficiency. Furthermore, the hollow fibers make it possible toabsorb and attenuate sound and vibration by the spaces inside thefibers. Therefore, the application of the holding seal material 4 usingthese makes it possible to achieve a catalyst converter 1 that isexcellent in noise insulating and vibration insulating properties.

In accordance with the manufacturing method of the embodiment accordingto the third group of the present invention, a spinning stock solution18 is discharged through the metal mouth 19 a of a nozzle 19 having anon-circular shape in its cross-section. Immediately after dischargedfrom the metal mouth 19 a, the precursor fiber 6A has a cross-sectionalshape to which the cross-sectional shape of the metal mouth 19 a isreflected in a certain degree. However, as time has elapsed since thedischarge, the cross-sectional shape thereof tends to have a roundness(in other words, is subjected to the Barus' effect) due to the influenceof a surface tension exerted on the precursor fiber 6A so that thecross-section of the precursor fiber 6A comes to have a circle-wiseshape. Therefore, in the embodiment according to the third group of thepresent invention, dry hot air is blown thereto in a state immediatelyafter the discharge so that the precursor fiber 6A is dried andsolidified by being removed its moisture in the precursor fiber 6A.Consequently, it becomes possible to maintain a desired cross-sectionalshape given by the metal mouth 19 a, and consequently to obtain analumina-silica based fiber 6 having a non-circular sectional shapecomparatively easily. In other words, this manufacturing method is adesirable method to obtain the above-mentioned holding seal material 4.

In accordance with the manufacturing method of the embodiment accordingto the third group of the present invention, the dry hot air is blown ina forward direction with respect to the discharging direction of theprecursor fiber 6A so that the fiber 6A is dried and solidified, andalso extended simultaneously. Moreover, by carrying out the extendingprocess in this manner, it becomes possible to control the fiberdiameter and shape comparatively easily. Therefore, it is possible tomanufacture desired alumina-silica based fibers 6 easily as well aseffectively.

In accordance with the manufacturing method of the embodiment accordingto the third group of the present invention, a water-soluble plasticizeris preliminarily added to the spinning stock solution 18 so that theelastic modulus of the spinning stock solution 18 becomes smaller withthe Barus' effect being reduced. Therefore, the discharge behavior ofthe spinning stock solution 18 at the time of the spinning process isstabilized. Consequently, the precursor fiber 6A becomes lesssusceptible to thread breakage even when it is extended with a strongtension, and the fiber cross-sectional shape becomes less susceptible toroundness due to elastic deformation. Moreover, the above-mentionedplasticizer has a water-soluble property so that it is dispersed in thespinning stock solution 18 evenly. Thus, it becomes possible to reducethe Barus' ratio to a virtually fixed value, and consequently to obtaina fiber having the target fiber diameter and cross-sectional shapecomparatively easily. Therefore, it becomes possible to manufacturedesired alumina-silica based fibers 6 easily as well as effectively.

Moreover, the third group of the present invention may include aceramic-fiber-use spinning device that is used for forming the ceramicfibers according to the holding seal material of the third group of thepresent invention, that is, a ceramic-fiber-use spinning device whichincludes a nozzle having a metal mouth having a non-circularcross-sectional shape, and a flow path through which dry hot air issupplied, with a hot-air discharging port being formed in the vicinityof the metal mouth, and which is arranged so as to blow dry hot airthrough the above-mentioned hot-air discharging port in a forwarddirection with respect to the discharging direction of the ceramicprecursor fibers.

Here, the embodiment according to the third group of the presentinvention has exemplified a case in which the holding seal material 4according to the third group of the present invention is applied to acatalyst converter 1 used for an exhaust-gas-purifying device. However,the holding seal material 4 according to the third group of the presentinvention may of course be applied to devices other than the catalystconverter 1 used for an exhaust-gas-purifying device, such as a dieselparticulate filter (DPF) and a catalyst converter used for a fuel cellmodifier.

The following description will be given of an embodiment according to afourth group of the present invention.

Referring to FIGS. 1 to 3, the following description will be given of acatalyst converter used for an automobile exhaust gas purifying devicein accordance with an embodiment according to the fourth group of thepresent invention in detail.

The catalyst converter 1 in accordance with the embodiment of the fourthgroup of the present invention, shown in FIG. 3, is virtually the sameas the catalyst converter according to the first group of the presentinvention, and constituted by a catalyst carrier 2, a metal shell 3covering the outer circumference of the catalyst carrier 2, and aholding seal material 4 that is placed in a gap between the two members2 and 3.

Here, with respect to the catalyst carrier 2 and the metal shell 3, thesame members that have been explained in the catalyst converteraccording to the first group of the present invention may be used;therefore, the description thereof is omitted.

Moreover, with respect to the catalyst carrier 2, in addition to acordierite carrier molded into a honeycomb shape shown in theembodiment, for example, a honey comb porous sintered body and the likeof, for example, silicon carbide or silicon nitride and the like, may beused.

Furthermore, as shown in the catalyst carrier 20 shown in FIG. 4, thosehaving no sealing member may be used.

As shown in FIG. 1, the holding seal material 4 is a mat-shaped memberhaving an elongated shape, and a convex fitting section 11 is placed onits one end, and a concave fitting section 12 is placed on the otherend. As shown in FIG. 2, upon wrapping onto the catalyst carrier 2, theconvex fitting section 11 is just engaged by the concave fitting section12.

The holding seal material 4 in accordance with the embodiment accordingto the fourth group of the present invention is constituted by ceramicfibers aggregated into a mat shape (that is, a fiber aggregation)serving as a main element. With respect to the above-mentioned ceramicfibers, in the embodiment according to the fourth group of the presentinvention, alumina-silica based fibers 6 are used. In this case, thealumina-silica based fibers 6, which have a mullite crystal content in arange of 0% by weight or more to 10% by weight or less, are preferablyused. The fibers having such a chemical composition make it possible toprovide excellent heat resistance and a high repulsive force uponapplication of a compressing load, because the amorphous componentthereof becomes smaller. Therefore, even when it is subjected to a hightemperature while being placed in the gap, the possibility of reductionin the face pressure to be generated is lowered.

The lower limit of a permissible range of alumina content in thealumina-silica based fibers 6 is set to 50% by weight with the upperlimit being set to 100% by weight, and the lower limit of a permissiblerange of silica content is set to 0% by weight with the upper limitbeing set to 50% by weight. Here, with respect to the alumina content,the lower limit is preferably set to 68% by weight with the upper limitbeing preferably set to 83% by weight, and with respect to the silicacontent, the lower limit is preferably set to 32% by weight with theupper limit being preferably set to 17% by weight; more specifically,the contents are more preferably set as Al₂O₃:SiO₂=72:28.

If alumina is less than 68% by weight, or if silica exceeds 32% byweight, it might be difficult to improve the heat resistance and therepulsive force upon application of a compressing load sufficiently. Ifalumina exceeds 83% by weight, or if silica is less than 17% by weightalso, it might be difficult to improve the heat resistance and therepulsive force upon application of a compressing load sufficiently.

The lower limit of the average fiber diameter of the alumina-silicabased fibers 6 is preferably set to 5 μm, with the upper limit being setto 15 μm, and the dispersion in the fiber diameter is preferably limitedto a range within ±3 μm. Further, the lower limit of the average fiberdiameter is more preferably set to 7 μm, with the upper limit being setto 12 μm, and the dispersion in the fiber diameter is more preferablylimited to a range within ±2 μm.

The average fiber diameter of less than 5 μm makes it difficult toprovide a sufficient face pressure due to a reduction in the strength ofthe fiber itself, and also causes a problem in which the fibers tend tobe inhaled by the respiratory organs. In the case of the average fiberdiameter exceeding 15 μm, when the fibers are formed into a mat-shapedfiber aggregation, its aeration resistance is reduced, resulting indegradation in the sealing property. In addition to this adverse effect,there might be degradation in the breaking strength. This adverse effectis considered to be caused by an increase in small scratches generatedby an increase in the fiber surface area. Additionally, in the casewhere the dispersion in the fiber diameter exceeds ±3 μm, the fiberstend to be accumulated unevenly, with the result that the positionaldependence of the basis weight becomes higher.

The lower limit of the average fiber length of the alumina-silica basedfibers 6 is preferably set to 5 mm, with the upper limit being set to 20mm, and the dispersion in the fiber length is preferably limited to arange within ±4 mm. Further, the lower limit of the average fiber lengthis more preferably set to 8 mm, with the upper limit being set to 13 mm,and the dispersion in the fiber diameter is more preferably limited to arange within ±2 μm.

The average fiber length of less than 5 mm causes a problem in which thefibers tend to be inhaled by the respiratory organs. Moreover, thisfiber no longer exhibits characteristics as the fiber, and when thefibers are formed into a mat-shaped fiber aggregation, the fibers arenot allowed to entangle with one another preferably, making it difficultto obtain a sufficient face pressure. The average fiber length exceeding20 mm makes the fibers entangled with one another too strongly, with theresult that the fibers tend to be accumulated unevenly when the fibersare formed into a mat-shaped aggregation. In other words, the positionaldependence of the basis weight becomes higher, causing an adverse effectto the reduction in the dispersions in the face pressure value.Moreover, in the case where the dispersion in the fiber length exceeds±4 mm also, the fibers tend to be accumulated unevenly, causing thepositional dependence of the basis weight to become higher.

The content of shot in the holding seal material 4 is preferably set to3% by weight or less, more preferably 0% by weight, that is, no shotcontained at all.

When shot is contained, the positional dependence of the basis weightbecomes higher, causing an adverse effect to inhibit the reduction inthe dispersions in the face pressure value.

Moreover, the tensile strength of each of the alumina-silica basedfibers 6 is preferably set to 0.1 GPa or more, more preferably 0.5 GPaor more. In addition to a complete round shape, the cross-sectionalshape of each the alumina-silica based fibers 6 may be set to a deformedcross-sectional shape (for example, an elliptical shape, an elongatedcircular shape, or a virtually triangular shape).

In the catalyst converter according to the fourth group of the presentinvention, the thickness of the holding seal material 4 prior to theassembling process, the GBD (bulk density) of the holding seal material4 after the assembling process and the initial face pressure of theholding seal material 4 in the assembled state are preferably set in thesame manner as those described in the catalyst converter according tothe first group of the present invention; therefore, the descriptionthereof is omitted.

Here, such a holding seal material 4 may be subjected to a needlepunching process, a resin impregnation process, etc., if necessary. Byapplying these processes, it becomes possible to compress the holdingseal material 4 in the thickness direction, and consequently to make itthinner.

The following description will be given of a sequence of processes formanufacturing a catalyst converter 1 according to the fourth group ofthe present invention.

First, a spinning stock solution is prepared by mixing an aluminum saltaqueous solution, silica sol and an organic polymer. In other words, thespinning stock solution is prepared by using an inorganic salt method.The aluminum salt aqueous solution, which serves as an alumina source,also serves as a component giving viscosity to the spinning stocksolution.

With respect to such an aqueous solution, an aqueous solution of basicaluminum salt is preferably selected. The silica sol, which serves as asilica source, also serves as a component for giving high strength tothe fibers. The organic polymer is a component for giving afiber-drawing property to the spinning stock solution.

An antifoamer, etc. may be added to the spinning stock solution. Here,by altering the ratio of the aluminum salt and silica sol, it becomespossible to control the chemical composition of the alumina-silica basedfibers 6 to a certain extent.

Moreover, not limited to those exemplified here, the composition of thespinning stock solution may be desirably changed as long as it does notcause great degradation in the spinning property and physical propertiesof the fibers.

Next, the resulting spinning stock solution is condensed under vacuum toprepare a spinning stock solution that has been prepared to have adensity, temperature, viscosity and the like suitable for the spinning.In this case, the spinning stock solution, which has had approximately aconcentration of 20% by weight, is preferably condensed to have 30 to40% by weight. Moreover, the viscosity is preferably set to 10 to 2000Poise.

Moreover, the spinning stock solution thus prepared is continuouslydischarged into the air through a nozzle of a spinning device, and takenup while the resulting precursor fiber being extended. In this case, forexample, a dry-type pressurizing spinning method may be preferably used.

Incidentally, by properly setting the cross-sectional shape and size ofthe nozzle discharging port, with the discharging, extending andtaken-up conditions being set to fixed states, it becomes possible tocontrol the fiber diameter in a narrow range. This arrangement makes itpossible to reduce dispersions in the fiber diameter.

Successively, the long fibers of the precursor fibers, obtained throughthe above-mentioned processes, are chopped to a length set toapproximately 0.5 to 10 mm so as to form short fibers. The advantages ofsuch a short-fiber-spinning method are to make the dispersion of thefiber length smaller by controlling the fiber length in a narrow range,and to preliminarily avoid the occurrence of shot. In other words, thelength of the resulting short fibers is basically dependent on themechanical precision of the cutting device with very small width ofdispersions.

Further, with respect to the cutting device, for example, a guillotinecutter or other mechanical cutting devices may be used to cut the longfibers.

Thereafter, the short fibers are collected, untied and laminated, or afiber-dispersed solution, obtained by dispersing the short fibers inwater, is poured into a mold, and pressed and dried so that a mat-shapedfiber aggregation is obtained.

Next, the mat-shaped fiber aggregation is sintered through a firing stepto be formed into ceramics (crystallized) so that the precursor fiber ishardened to obtain an alumina-silica based fiber 6.

In the above-mentioned firing step, it is preferable to set the firingcondition so as to make the mullite crystal content in the resultingalumina-silica based fibers 6 at 10% by weight or less. For example, thefiring temperature in the firing step is preferably set in a range of1000 to 1300° C. The firing temperature of less than 1000° C. fails tocompletely dry and sinter the precursor fibers, with the result that itbecomes difficult to securely provide excellent heat resistance and ahigh repulsive force at the time of application of a compressing load tothe holding seal material 4. In contrast, in the case of a firingtemperature exceeding 1300° C., the mullite crystallization in thealumina-silica based fiber 6 is allowed to easily progress. For thisreason, it becomes difficult to reduce the mullite crystal content to10% by weight or less, and consequently, it may not be able to securelyprovide excellent heat resistance and a high repulsive force at the timeof application of a compressing load to the holding seal material 4.

Here, instead of the above-mentioned method in which the long fibers ofthe precursor fibers are chopped into short fibers, and then fired, thefiring step may be preliminarily carried out before the chopping processof the long fibers into short fibers.

Further, the fiber aggregation is punched out into a predetermined shapeto form a holding seal material 4. Then, after the holding seal material4 has been impregnated with an organic binder, if necessary, the holdingseal material 4 may be further compressed, and molded in the thicknessdirection. With respect to the organic binder used in this case,polyvinyl alcohol, acrylic resin and the like may be used, in additionto latex and the like such as acrylic rubber and nitrile rubber and thelike.

Moreover, the holding seal material 4 is wrapped around the outercircumferential face of the catalyst carrier 2 and secured by theorganic tape 13. Thereafter, this is subjected to a press-fitting,canning or wrap-tightening process to complete a desired catalystconverter 1.

Consequently, in accordance with the embodiment according to the fourthgroup of the present invention, the following effects can be obtained.

In the holding seal material 4 of the embodiment according to the fourthgroup of the present invention, the dispersion in the fiber diameter ofthe alumina-silica based fibers 6 is reduced within a range of ±3 μmwith the dispersion in the fiber length thereof being reduced within arange of ±4 mm, and the content of shot is set to 3% by weight or less.Therefore, with these synergistic effects, it is possible to extremelyreduce the positional dependence of the basis weight, and also to reducedispersions in the face pressure effectively. Thus, it becomes possibleto achieve a holding seal material 4 that is stable in quality.

In accordance with the holding seal material 4 according to the fourthgroup of the present invention, in addition to the effect that reducesthe dispersion in the face pressure, it is also possible to improve theface pressure value; therefore, it becomes possible to reduce thequantity of the alumina-silica based fibers 6 required for manufacturinga sheet of holding seal material 4. Thus, it becomes possible to reducethe costs of the holding seal material 4.

In accordance with the manufacturing method of the embodiment accordingto the fourth group of the present invention, since the spinning processis carried out by using an inorganic salt method, it is possible tocontrol the fiber diameter in a narrow range, and consequently to reducedispersions in the fiber diameter. Moreover, this method chops longfibers to obtain short fibers; therefore, different from a method inwhich fibers are obtained through a blowing process, it is possible tocontrol the fiber length in a narrow range. Thus, it becomes possible toreduce dispersions in the fiber length. In addition to these effects, itis also possible to avoid the generation of shot. Consequently, thismanufacturing method makes it possible to obtain the above-mentionedholding seal material 4 securely with ease.

As clearly described above, the manufacturing method of the embodimentaccording to the fourth group of the present invention makes it possibleto provide a desirable method to obtain the above-mentioned holding sealmaterial 4.

The manufacturing method of the holding seal material according to thefourth group of the present invention may include a method for firingthe produced ceramic short fibers as one of the inventions of the fourthgroup; that is, a ceramic short fiber producing method which includes aspinning process in which a spinning stock solution containing analuminum salt aqueous solution, silica sol and an organic polymer iscontinuously discharged from a nozzle to obtain a long fiber of aprecursor fiber, a cutting process for chopping the above-mentioned longfiber into a predetermined length to obtain short fibers, and a firingstep for heating and sintering the above-mentioned short fibers. Thismethod relates to a manufacturing method of ceramic short fibers whichcan reduce dispersions in the fiber length and fiber diameter.

Moreover, the embodiment according to the fourth group of the presentinvention has exemplified a case in which the holding seal material 4according to the fourth group of the present invention is applied to acatalyst converter 1 used for an exhaust-gas-purifying device; however,the holding seal material 4 according to the fourth group of the presentinvention may of course be applied to devices other than the catalystconverter 1 used for an exhaust-gas-purifying device, such as a dieselparticulate filter (DPF), a catalyst converter and the like used for afuel cell modifier.

The following description will be given of embodiments according to afifth group of the present invention.

First Embodiment

Referring to FIGS. 1 to 3, as well as FIG. 12, the following descriptionwill be given of a catalyst converter used for an automobile exhaust gaspurifying device in accordance with the first embodiment according tothe fifth group of the present invention in detail.

This catalyst converter 1 in accordance with the embodiment of the fifthgroup of the present invention, shown in FIG. 3, is virtually the sameas the catalyst converter according to the first group of the presentinvention, and constituted by a catalyst carrier 2, a metal shell 3covering the outer circumference of the catalyst carrier 2, and aholding seal material 4 that is placed in a gap between the two members2 and 3.

Here, with respect to the catalyst carrier 2 and the metal shell 3, thesame members that have been explained in the catalyst converteraccording to the first group of the present invention may be used;therefore, the description thereof is omitted.

Moreover, with respect to the catalyst carrier 2, in addition to acordierite carrier molded into a honeycomb shape shown in theembodiment, for example, a honey comb porous sintered body of, forexample, silicon carbide or silicon nitride and the like, may be used.

Furthermore, as shown in the catalyst carrier 20 shown in FIG. 4, thosehaving no sealing member may be used.

As shown in FIG. 1, the holding seal material 4 is a mat-shaped memberhaving an elongated shape, and a convex fitting section 11 is placed onits one end, and a concave fitting section 12 is placed on the otherend. As shown in FIG. 2, upon wrapping onto the catalyst carrier 2, theconvex fitting section 11 is just engaged by the concave fitting section12.

The holding seal material 4 in accordance with the embodiment accordingto the fifth group of the present invention is constituted by ceramicfibers aggregated into a mat shape (that is, a fiber aggregation)serving as a main element. With respect to the above-mentioned ceramicfibers, in the embodiment according to the fifth group of the presentinvention, alumina-silica based fibers 6 are used. In this case, thealumina-silica based fibers 6, which have a mullite crystal content in arange of 0% by weight or more to 10% by weight or less, are preferablyused. The fibers having such a chemical composition make it possible toprovide excellent heat resistance and a high repulsive force uponapplication of a compressing load, because the amorphous componentthereof becomes smaller. Therefore, even when it is subjected to a hightemperature while being placed in the gap, the possibility of reductionin the face pressure to be generated is comparatively lowered.

The chemical composition of the alumina-silica based fibers 6 ispreferably set so that alumina is in a range of 68 to 83% by weight andsilica is in a range of 32 to 17% by weight, more specifically,Al₂O₃:SiO₂=72:28.

If alumina is less than 68% by weight, or if silica exceeds 32% byweight, it might be difficult to improve the heat resistance and therepulsive force upon application of a compressing load sufficiently. Inthe case where alumina exceeds 83% by weight, or in the case wheresilica is less than 17% by weight also, it might be difficult tosufficiently improve the heat resistance and the repulsive force uponapplication of a compressing load.

As schematically shown in FIG. 12, in the case of the alumina-silicabased fibers 6 constituting this holding seal material 4, the fibers arepartially bonded to each other by a ceramic adhesive 7. Thus, it ispossible to provide a structure wherein, so to speak, a cross-linkingbridge is placed between portions at which ceramic fibers are adjacentto each other with overlapped parts. In other words, the holding sealmaterial 4 is constituted by the alumina-silica based fibers 6 having abranched structure.

Here, there are voids inside the holding seal material 4.

Moreover, instead of the exemplified alumina-silica based fibers 6, forexample, other ceramic fibers such as crystalline alumina fibers andsilica fibers and the like may be used to form the holding seal material4.

The ceramic adhesive 7 preferably comprises a substance that constitutesthe ceramic fibers. The above-mentioned ceramic adhesive 7 of thischaracteristics has a high affinity to the fibers, and allows the bondedportions to have high strength; thus, it becomes possible to securelyprevent degradation with time in the face pressure. For this reason, inthe embodiment according to the fifth group of the present invention,the ceramic adhesive 7 mainly composed of alumina is adopted.

Moreover, with respect to the ceramic adhesive 7, a substance that doesnot constitute the ceramic fibers may be adopted. For example, in thecase where the alumina-silica based fibers 6 are selected, a ceramicadhesive 7 made of zirconia, titania, yttria, ceria, calcia, or magnesiaand the like may be used.

The lower limit of the content of the ceramic adhesive 7 is preferablyset to 1% by weight with the upper limit thereof being set to 8% byweight, and the lower limit thereof is more preferably set to 3% byweight with the upper limit being set to 7% by weight.

When the above-mentioned content is less than 1% by weight, the fibersmight not be bonded to one another with high strength. In contrast, inthe case where the above-mentioned content exceeds 8% by weight,although the problem with the bonding strength is solved, the voidsinside the holding seal material 4 tend to be filled, failing to providedesired physical properties, that is, elasticity and heat-insulatingproperty, to the holding seal material 4.

With respect to the average fiber diameter and average fiber length ofthe alumina-silica based fibers 6, these factors are preferably set inthe same manner as those explained in the catalyst converter accordingto the first group of the present invention; therefore, the descriptionthereof is omitted.

Moreover, the tensile strength (relative strength) of each fiber of thealumina-silica based fibers 6 is preferably set to 0.1 GPa or more, morepreferably 0.5 GPa or more. In addition to a complete round shape shownin FIG. 12, the cross-sectional shape of the alumina-silica based fibers6 may be set to a deformed cross-sectional shape (such as an ellipticalshape, an elongated circular shape and a generally-triangular shape).

With respect to the catalyst converter according to the fifth group ofthe present invention, the thickness of the holding seal material 4prior to the assembling process, the GBD (bulk density) of the holdingseal material 4 after the assembling process and the initial facepressure of the holding seal material 4 in the assembled state arepreferably set in the same manner as those described in the catalystconverter according to the first group of the present invention;therefore, the description thereof is omitted.

Here, the holding seal material 4 may be subjected to a needle punchingprocess, a resin impregnation process and the like, if necessary. Theapplication of these processes makes it possible to compress the holdingseal material 4 in the thickness direction and consequently to make itthinner.

Next, an explanation will be given on the sequence of processes formanufacturing a catalyst converter 1 according to the fifth group of thepresent invention.

First, a spinning stock solution is prepared in the same manner asexplained in the catalyst converter manufacturing method according tothe fourth group of the present invention, and long fibers of precursorfibers are formed.

Then, the precursor fibers are formed into ceramics (crystallized) bycarrying out a first firing step to harden the precursor fibers; thus,alumina-silica based fibers 6 are obtained.

In the above-mentioned firing step, it is preferable to set the firingcondition so as to make the mullite crystal content in the resultingalumina-silica based fibers 6 having 10% by weight or less. For example,the firing temperature in the firing step is preferably set in a rangeof 1000 to 1300° C. The firing temperature of less than 1000° C. failsto completely dry and sinter the precursor fibers, with the result thatit may not be able to securely provide excellent heat resistance and ahigh repulsive force at the time of application of a compressing load tothe holding seal material 4. In contrast, in the case of a firingtemperature exceeding 1300° C., the mullite crystallization in thealumina-silica based fiber 6 is allowed to easily progress. For thisreason, it becomes difficult to reduce the mullite crystal content to10% by weight or less, and consequently, it becomes difficult tosecurely provide excellent heat resistance and a high repulsive force atthe time of application of a compressing load to the holding sealmaterial 4.

Successively, the long fibers of the alumina-silica based fibers 6,obtained through the above-mentioned processes, are chopped to apredetermined length by using, for example, guillotine cutter, to formshorter fibers in a certain extent. Thereafter, the short fibers arecollected, untied and laminated, or a fiber-dispersed solution, obtainedby dispersing the short fibers in water, is poured into a mold, andpressed and dried so that a mat-shaped fiber aggregation is obtained.Further, this fiber aggregation is punched out into a predeterminedshape to form a holding seal material 4.

After the above-mentioned molding process, a bonding process is carriedout so that the above-mentioned short fibers constituting a fiberaggregation are mutually bonded by a ceramic adhesive 7. Morespecifically, the following processes are carried out.

First, a material solution of the ceramic adhesive 7 is prepared, andsupplied between short fibers that constitute the aggregation. In otherwords, in the first step of the bonding processes, a liquid-statesubstance supplying process in which a liquid-state substance issupplied between the short fibers constituting the aggregation so thatthe liquid-state substance that is formed into a ceramic adhesive 7later is allowed to adhere to portions at which the precursor fibersconstituting the above-mentioned aggregation are adjacent to each otherwith overlapped parts, is carried out. In this case, with respect to theabove-mentioned material solution, for example, a water-soluble metalsolution such as a water solution of aluminum chloride is preferablyused. Here, a water solution of aluminum salt other than chlorides, thatis, a water solution other than a water solution of aluminum chloridecontaining aluminum ions, may be used. Additionally, a water solutioncontaining metal cations other than aluminum ions, such as a watersolution of zirconium chloride, a water solution of titanium chlorideand a water solution of chromium chloride and the like may be selected.

Here, in place of a basic water solution of aluminum chloride, forexample, the spinning stock solution of the alumina-silica based fibersmay be commonly used so as to carry out the bonding process. In thiscase as well, the ceramic adhesive 7 made from the fiber-constitutingsubstance may be prepared.

The above-mentioned water-soluble metal solution is preferably set tohave a low viscosity, more specifically, approximately, 0.1 to 10centipoise. The water-soluble metal solution having a low viscosityeasily has a surface tension exerted thereon, with the result that it ispossible to provide a better adhesive property to portions in whichshort fibers are adjacent with each other with overlapped parts.Moreover, when the viscosity is too high, it becomes difficult to allowthe solution to securely enter the inside of the fiber aggregationevenly.

The lower limit of the quantity of supply of the water-soluble metalsolution in the fiber aggregation is set to 1% by weight, with the upperlimit thereof being set to 10% by weight, and more preferably, the lowerlimit thereof is set to 2% by weight with the upper limit thereof beingset to approximately 8% by weight. The quantity of supply of less than1% by weight causes an insufficient quantity of the solution to adhereto the portions at which the fibers are adjacent to each other withoverlapped parts, sometimes failing to mutually bond the fibersstrongly. In contrast, the quantity of supply exceeding 10% by weightcauses the voids inside the holding seal material 4 to be easily filledwith the excessive solution, sometimes impairing desired physicalproperties in the holding seal material 4.

Examples of the method for supplying a material solution to the fiberaggregation include a method in which the fiber aggregation is immersedinto a solution so that the inside thereof is impregnated with thesolution, a method in which a solution in a mist state is supplied intothe fiber aggregation by using a spray atomizing process, a method inwhich a solution is dipped and supplied into the fiber aggregation andthe like. Among these, the impregnation method is preferably used. Theimpregnation method makes it possible to allow the material solution tosecurely enter the inside of the fiber aggregation evenly.

After the impregnation process, it is preferable to heat and dry thefiber aggregation. The heating and drying processes make it possible toremove excessive moisture in the material solution to a certain degree,and consequently to carry out a firing step in the next process in astable manner.

Next, the dried fiber aggregation is again fired at a high temperature,and the metal component in the material solution, adhered to the mutualadjacent portions of the short fibers, is sintered and formed intoceramics; thus, a cross-linking bridge made from the ceramic adhesive 7is formed at the corresponding portion so that the short fibers arebonded to each other.

Thereafter, the holding seal material 4 is impregnated with an organicbinder, if necessary, and the holding seal material 4 may be compressedand molded in a thickness direction. In this case, with respect to theorganic binder, polyvinyl alcohol, acrylic resin and the like may beused, in addition to latexes such as acrylic rubber, nitrile rubber andthe like.

Then, the holding seal material 4, obtained by punching out theabove-mentioned fiber aggregation into a predetermined shape, is woundaround the outer circumferential face of the catalyst carrier 2 andsecured by the organic tape 13. Thereafter, this is subjected to apress-fitting, canning or wrap-tightening process to complete a desiredcatalyst converter 1.

Therefore, in accordance with the first embodiment according to thefifth group of the present invention, the following effects can beobtained.

In accordance with the first embodiment according to the fifth group ofthe present invention, the holding seal material 4 makes it possible toprovide a structure wherein, so to speak, a cross-linking bridge isplaced between portions at which ceramic fibers are adjacent to eachother with overlapped parts by using the ceramic adhesive 7, andconsequently to make the respective fibers less susceptible to slidingand deviation.

Therefore, even when an external load is imposed thereon in a manner soas to compress the holding seal material 4 for a long time, thisstructure is less susceptible to degradation in the face pressure.Moreover, in this holding seal material 4, since the short fibers arepartially bonded to each other so that the voids inside the holding sealmaterial 4 are not completely filled. Therefore, physical properties(elasticity, heat-insulating property, and the like), inherentlyrequired for the holding seal material 4, are maintained. Moreover, theceramic adhesive 7, which is used as the crosslinking bridge, isexcellent in heat resistance. Therefore, even when the holding sealmaterial 4 is subjected to a high temperature of approximately 1000° C.during use, the bonding portions are less susceptible to degradation instrength, and this advantage also makes it possible to prevent areduction in the face pressure.

In accordance with the first embodiment according to the fifth group ofthe present invention, the alumina-silica based fibers 6 are selected,and the ceramic adhesive 7 mainly composed of alumina is also selected.In other words, the ceramic adhesive 7 comprises a substanceconstituting the alumina-silica based fibers 6. For this reason, thisadhesive provides very high affinity for the corresponding fibers, andconsequently increases the strength of the bonded portions. Therefore,this combination makes it possible to securely prevent degradation withtime in the face pressure. Further, the application of thealumina-silica based fibers 6 having excellent heat resistance makes itpossible to reduce degradation with time in the face pressure at hightemperatures.

In the first embodiment according to the fifth group of the presentinvention, the content of the ceramic adhesive 7 is set in theabove-mentioned preferable range. Therefore, it becomes possible toprovide high strength in the bonded portions while maintaining desiredproperties in the holding seal material 4.

In accordance with the first embodiment according to the fifth group ofthe present invention, upon manufacturing the holding seal material 4,the firing step and bonding process of the precursor fibers are carriedout in a separated manner. More specifically, the bonding process iscarried out after the firing step of the precursor fibers. For thisreason, it is possible to securely provide alumina-silica based fibers 6having a better shape in comparison with a case in which both of theprocesses are carried out simultaneously so that the above-mentionedalumina-silica based fibers 6 having a desired shape are securely bondedto each other. Therefore, it becomes possible to securely manufacture aholding seal material 4 that is less susceptible to degradation withtime in the face pressure easily.

Second Embodiment

The following description will be given of a second embodiment accordingto the fifth group of the present invention. Here, explanations will bemainly given on points that are different from the first embodimentaccording to the fifth group of the present invention, and those sameparts are indicated by the same reference numerals, and the descriptionthereof is omitted.

In this case, a holding seal material 4 having the above-mentionedstructure is manufactured in the following sequence. First, a spinningprocess is carried out in the same manner as the first embodimentaccording to the fifth group of the present invention to provide longfibers of precursor fibers by using a spinning stock solution of thealumina-silica based fibers 6 as a material. Next, a cutting process iscarried out so that the long fibers are chopped by a guillotine cutterto form shorter fibers in a certain extent. Then, a molding process iscarried out in such a manner that the short fibers are collected, untiedand laminated; or a fiber-dispersed solution, obtained by dispersing theshort fibers in water, is poured into a mold, and pressed and dried, sothat a mat-shaped fiber aggregation is obtained. Next, a liquid-statesubstance supplying process is carried out in such a manner that theliquid-state substance, which forms ceramic adhesive 7 later, is allowedto adhere to portions at which the precursor fibers constituting thefiber aggregation are adjacent to each other with overlapped parts.Next, in a sintering step, the fiber aggregation is heated so that theprecursor fibers and the liquid-state substance are simultaneouslysintered. Lastly, the fiber aggregation is subjected to a punchingprocess and the like to provide a holding seal material 4.

In other words, in contrast to the first embodiment according to thefifth group of the present invention in which the liquid-state-substancesupplying process is carried out in a stage after the firing step (afterthe fibers have been formed into ceramics), the second embodimentaccording to the fifth group of the present invention carries out thisprocess in a stage prior to the firing step (in a state of un-sinteredprecursor fibers), which forms a great difference from the firstembodiment.

With respect to the specific example of the liquid-state substancesupplying process, the following two methods are listed.

In the first method, a fiber aggregation, made from precursor fibers ofthe alumina-silica based fibers 6, is placed under a highly moistenedenvironment with high moisture so that the liquid-state substance issupplied thereto. In this case, vapor, existing under the highlymoistened environment, is allowed to securely enter the inside of thefiber aggregation, and then condensed into moisture. Moreover, themoisture is allowed to selectively adhere to the adjacent overlappedparts of the fibers by a function of surface tension. Here, theprecursor fibers of the alumina-silica based fibers 6 are water-soluble.For this reason, the adhesion of moisture causes the surface of theprecursor fibers at the adjacent overlapped parts to be dissolved to acertain extent. Since the liquid-state substance, generated by suchdissolution, has virtually the same composition as the alumina-silicabased fibers 6, it is actually allowed to form a ceramic adhesive 7later. Therefore, when a firing step is carried out at a temperature ina range of 1000 to 1300° C., the precursor fibers and the liquid-statesubstance are simultaneously sintered to form ceramics, with the resultthat a cross-linking bridge made from the ceramic adhesive 7 is formedbetween the alumina-silica based fibers 6. Here, in this method, theconditions (for example, the quantity of vapor, processing temperature,processing time, etc.) need to be set to a level that does not causeover-dissolution of the precursor fibers. Therefore, in the case wheremoisture is directly supplied through an atomizing process and the like,it is necessary to take over-dissolution into consideration.

The second method is characterized in that a non-aqueous liquid-statesubstance containing the same inorganic element contained in thealumina-silica based fibers 6 is sprayed onto the fiber aggregationcomposed of the precursor fibers of the alumina-silica based fibers 6 sothat the corresponding substance is supplied thereto. In this case, thesprayed non-aqueous liquid-state substance is allowed to securely enterthe inside of the fiber aggregation, and also to selectively adhere tothe adjacent overlapped portions between the fibers through a functionof surface tension. With respect to the non-aqueous liquid-statesubstance, for example, commercially available non-aqueous silicone oilsand the like are listed. Since the silicon oil contains silicon (Si)that is an inorganic element contained in the alumina-silica basedfibers 6, this is allowed to actually form the ceramic adhesive 7 later.

Therefore, when a firing step is carried out at a temperature of 1000 to1300° C., the precursor fibers and the non-aqueous liquid-statesubstance are simultaneously sintered to form ceramics, with the resultthat a cross-linking bridge made from the ceramic adhesive 7 is formedbetween the alumina-silica based fibers 6. In this case, the ceramicadhesive 7 is an oxide of silicon (silica: SiO₂). Here, in addition tothe non-aqueous silicone oil, for example, a material, formed bydissolving, for example, TEOS (ethyl silicate) in oil, may be used.

In accordance with the second embodiment according to the fifth group ofthe present invention, the following effects can be obtained.

In the manufacturing method of the second embodiment according to thefifth group of the present invention, the firing step and bondingprocess of the precursor fibers are carried out simultaneously;therefore, in comparison with the manufacturing method of the firstembodiment according to the fifth group of the present invention inwhich these processes are carried out simultaneously, it is possible toreduce the number of heating steps. Thus, it becomes possible to reducethermal energy to be applied thereto, and consequently to reduce themanufacturing costs. Therefore, it becomes possible to manufacture aholding seal material 4 that is less susceptible to degradation withtime in the face pressure efficiently at low costs.

In the case where the first method is adopted, the liquid-statesubstance to be formed into the ceramic adhesive 7 later is allowed tosecurely adhere to the adjacent overlapped portions. Moreover,basically, the above-mentioned liquid-state substance, which is afiber-dissolved substance, has virtually the same composition as thealumina-silica based fibers 6.

For this reason, the above-mentioned liquid-state substance has a highaffinity for the precursor fibers, and makes it possible to securelybond the fibers to each other with high strength. Therefore, it ispossible to securely prevent degradation with time in the face pressure.

The application of the second method also allows the liquid-statesubstance that forms the ceramic adhesive 7 later to securely adhere toportions at which the fibers are adjacent to each other with overlappedparts. Further, in this case, a non-aqueous liquid-state substance isused. For this reason, even when this adheres to the precursor fibers ofthe alumina-silica based fibers 6 having a water-soluble property, theprecursor fibers are not dissolved. Therefore, it is not necessary toworry about degradation in the strength of the alumina-silica basedfibers 6 itself due to too much dissolution of the precursor fibers, andit is not particularly necessary to set specific conditions carefullyfor preventing over-dissolution. Consequently, it is possible tomanufacture a holding seal material 4 comparatively easily. Moreover,since the above-mentioned liquid-state substance contains the inorganicelement contained in the alumina-silica based fibers 6, it has a highaffinity for the precursor fibers so that the fibers are securely bondedto each other with high strength. Thus, it becomes possible to securelyprevent degradation with time in the face pressure.

In the manufacturing method of the second embodiment according to thefifth group of the present invention, a cutting process is carried outbetween the spinning process and the molding process so that the longfibers of the precursor fibers are mechanically cut into a predeterminedlength so as to obtain short fibers. In other words, the manufacturingmethod of the second embodiment according to the fifth group of thepresent invention is different from the manufacturing method of thefirst embodiment according to the fifth group of the present inventionwhich carries out a cutting process after the firing step in that thecutting process is carried out prior to the firing step.

In the case where the cutting process is carried out after the sinteringstep of the precursor fibers as in the case of the manufacturing methodof the first embodiment according to the fifth group of the presentinvention, the alumina-silica based fibers 6 tend to have cracks andsplinters on the cut portion of the alumina-silica based fibers 6 due toan impact at the time of the cutting process. This is because, ingeneral, when precursor fibers are sintered to form ceramics, the fibersbecome brittle although they become hard. Consequently, thealumina-silica based fibers 6 come to have unstable end shapes, and themechanical strength of the fibers is lowered.

In contrast, since the precursor fibers are unsintered and comparativelysoft, they are less susceptible to cracks and the like on the cutportion even when they are subjected to a mechanical impact at the timeof the cutting process. Therefore, the alumina-silica based fibers 6,obtained by sintering these, have stable end shapes, and are excellentin mechanical strength. Consequently, in accordance with the secondembodiment according to the fifth group of the present invention, it ispossible to improve the initial face pressure. The resulting propertyfor preventing the generation of cracks and the like is considered togive effects also on prevention of degradation with time in the facepressure to a certain degree.

Moreover, in accordance with the manufacturing method of the secondembodiment according to the fifth group of the present invention, sincethe cutting subject is each of the precursor fibers that are not sohard, the blades of a guillotine cutter serving as a mechanical cuttingdevice are less susceptible to damages and abrasion. Therefore, itbecomes possible to eliminate the necessity of frequently exchangingdeteriorated blades, and consequently to prevent an increase in therunning costs. Moreover, since it is not necessary to make the blades sohard, generally-used blades can be applied; thus, it becomes possible toprevent an increase in the facility costs.

Additionally, in the case where the second method is adopted in thesecond embodiment according to the fifth group of the present invention,a method which can replace the atomizing method upon supplying thenon-aqueous liquid-state substance, for example, a dipping method, maybe adopted. It is of course possible to vaporize and supply thenon-aqueous liquid-state substance.

Moreover, in the manufacturing method of the holding seal materialaccording to the fifth group of the present invention, the watersolution containing aluminum ions may be supplied as a basic watersolution of aluminum chloride or as the above-mentioned spinning stocksolution of the alumina-silica based fibers.

Furthermore, in the manufacturing method of the holding seal materialaccording to the fifth group of the present invention, the water-solublemetal solution may be prepared as a water solution containing at leastone material selected from the group consisting of aluminum chloride,zirconium chloride, titanium chloride and chromium chloride.

Here, the embodiment according to the fifth group of the presentinvention has exemplified a case in which the holding seal material 4according to the fifth group of the present invention is applied to acatalyst converter used for an exhaust-gas-purifying device; however,the holding seal material 4 according to the fifth group of the presentinvention may of course be applied to devices other than the catalystconverter 1 used for an exhaust-gas-purifying device, such as a dieselparticulate filter (DPF) and a catalyst converter used for a fuel cellmodifier.

The following description will be given of an embodiment according to asixth group of the present invention.

The manufacturing method of an alumina fiber aggregation according tothe sixth group of the present invention comprises: a spinning step ofobtaining a continuous long-fiber precursor by using an alumina fiberstock solution used in an inorganic salt method as a material; achopping step of cutting the continuous long-fiber precursor intoshort-fiber precursors; a mat preparing step of preparing a mat-shapedshort fiber precursor by using thus obtained said short-fiber precursor;and a firing step of firing the mat-shaped short fiber precursor tomanufacture an alumina fiber aggregation.

In the manufacturing method of an alumina fiber aggregation according tothe sixth group of the present invention, the firing step is carried outafter the spinning process, the chopping process and the mat-formingprocess so that it becomes possible to sufficiently increase themechanical strength of the alumina short fibers that are used in thealumina fiber aggregation to be manufactured, and also to manufacture analumina fiber aggregation that has a high initial face pressure, and isless susceptible to degradation with time in the face pressure.

The reason for this is explained as follows.

In other words, in the case where alumina short fibers to be used in analumina fiber aggregation are manufactured by using a conventionalmethod, a continuous long fiber precursor, obtained by carrying out aspinning process on an alumina-fiber stock solution, is fired to form analumina long fiber, and this alumina long fiber is then cut by using amechanical means such as a cutter to provide the alumina short fibers;however, the alumina short fibers thus manufactured tend to have burs onthe cut face thereof (see FIG. 15( b)).

Here, FIG. 15( a) shows an SEM photograph of a cross-sectional face ofone of the alumina short fibers used in an alumina fiber aggregationthat has been manufactured by a manufacturing method of an alumina fiberaggregation of the present invention, and FIG. 15( b) shows an SEMphotograph of a cross-sectional face of one of the alumina short fibersused in an alumina fiber aggregation that has been manufactured by aconventional method.

Upon cutting an alumina long fiber, one portion of the alumina longfiber tends to chip in the vicinity of the cut face, before theabove-mentioned cutter or the like has completely cut the alumina longfiber, and resulting chips adhere to the cut face to cause burs on thecut face of the alumina short fiber, as shown in FIG. 15( b).

When the alumina long fiber is cut by a mechanical means such as acutter, a great shearing stress is exerted on the cut face. However,since the above-mentioned alumina long fiber is made of hard, brittleceramics having a certain degree of strength, and the shearing stress,exerted on the cut face, causes chips on one portion of the alumina longfiber, and it is considered that the chips adhere to the cut face, withthe result that burs, shown in FIG. 15( b), are generated.

Moreover, a number of alumina short fibers to be used in an aluminafiber aggregation are entangled with one another in a complex manner;and when burs are generated on the cut face of each alumina short fiber,the burs cause damages to other alumina short fibers when they areentangled with one another in a complex manner.

When the above-mentioned alumina short fiber is observed in detail,there are portions on which micro-cracks are generated due to theabove-mentioned chips and burs, and there are other portions on whichmicro-cracks are generated due to forces that are imposed on the fiberat the time of the cutting process.

Therefore, these chips, burs, micro-cracks and the like cause a failureto provide sufficient mechanical strength in the alumina short fibers,and make the dispersions greater.

Here, the degradation with time in the initial face pressure and theface pressure of the alumina fiber aggregation is caused depending onthe mechanical strength of the alumina short fibers used in the aluminafiber aggregation, and when each alumina short fiber has excellentmechanical strength, the initial face pressure of the alumina fiberaggregation is maintained sufficiently high with the degradation withtime in the face pressure being reduced.

However, as described earlier, in the conventional alumina fiberaggregation, the mechanical strength of the alumina short fibers used inthe alumina fiber aggregation is not sufficiently high with highdispersions thereof; therefore, it is not possible to obtainsufficiently high initial face pressure in the alumina fiberaggregation, and it is considered that the degradation with time in theface pressure becomes comparatively greater.

In the manufacturing method of the alumina fiber aggregation accordingto the sixth group of the present invention, the continuous long fiberprecursor obtained from the spinning process is cut by a cutter or thelike without being subjected to a firing step so that a short fiberprecursor is formed. In other words, since the above-mentionedcontinuous long fiber precursor is only subjected to an extendingprocess after having been subjected to a spinning process, it is soft,and even when the continuous long fiber precursor is cut by a cutter orthe like, no chips are generated in the vicinity of the cut face due toa shearing stress exerted on the cut face (see FIG. 15( a)). Moreover,the cut face is less susceptible to micro-cracks.

Therefore, the alumina short fibers to be used in the alumina fiberaggregation which is manufactured later are allowed to have sufficientlyhigh mechanical strength with smaller dispersions thereof, in comparisonwith those alumina short fibers to be used in alumina fiber aggregationmanufactured in a conventional method. For this reason, the aluminafiber aggregation, manufactured through the manufacturing method of thealumina fiber aggregation in the present invention, is allowed to have ahigh initial face pressure, and less susceptible to degradation withtime.

The following description will be given of the manufacturing method ofan alumina fiber aggregation according to the sixth group of the presentinvention in detail.

In the manufacturing method of an alumina fiber aggregation according tothe sixth group of the present invention, first, a spinning process iscarried out to obtain a continuous long fiber precursor by using analumina-fiber stock solution to be used in an inorganic salt method as amaterial.

In the spinning process, first, the above-mentioned alumina-fiber stocksolution to be used in the inorganic salt method is prepared.

The above-mentioned alumina-fiber stock solution is prepared by usingthe inorganic salt method. More specifically, it is preferably preparedby mixing silica sol in a water solution of aluminum salt, since thismethod makes it possible to provide alumina fibers having high strength.

With respect to the above-mentioned water solution of aluminum salt, forexample, a water solution of basic aluminum salt may be selected. Here,the aluminum salt water solution serving as an alumina source is acomponent used for applying viscosity to the above-mentionedalumina-fiber stock solution.

Here, in this alumina-fiber stock solution, the ratio of mixing of thealuminum salt water solution and silica sol is preferably set to 40 to100% by weight of alumina and 0 to 60% by weight of silica in terms ofalumina and silica equivalent amount.

Moreover, an organic polymer may be added to such alumina fiber stocksolution, if necessary. Thus, it becomes possible to apply afiber-drawing property to the alumina-fiber stock solution.

With respect to the organic polymer, a straight-chain polymer containingcarbon, such as PVA (polyvinyl alcohol) and the like, may be used;however, in addition to this, any compound having a comparatively lowmolecular weight without a straight-chain structure (which is not apolymer) may be selected as long as it contains carbon.

Next, by condensing under vacuum the resulting spinning stock solution,the alumina-fiber stock solution is prepared so as to have aconcentration, temperature and viscosity suitable for the spinningprocess. In this case, the alumina-fiber stock solution, which has beennormally set to approximately a concentration of 20% by weight, ispreferably condensed to approximately 30 to 40% by weight. Moreover, theviscosity of the alumina-fiber stock solution after concentration undervacuum is preferably set to 1 to 200 Pa·s (10 to 2000 P).

Further, by discharging the alumina-fiber stock solution thus preparedinto a high-speed gas flow through a nozzle of a spinning device byusing a dry-type pressurizing spinning method and the like, a materialfiber, which has a cross-sectional shape that is analogous to the nozzlemetal mouth shape, is continuously obtained. The material fiber, thussubjected to the spinning process, is successively wound up while beingextended so that a continuous long-fiber precursor is obtained.

With respect to the shape of the opening of the nozzle, it is notparticularly limited, and any desired shape, such as a complete roundshape, a triangular shape, a Y-letter shape and a star shape, may beselected.

Moreover, the above-mentioned material fiber in the state of being spunout is preferably extended approximately 100 to 200 times to be formedinto a continuous long-fiber precursor. Thus, this is set to a range inwhich an alumina fiber having preferable strength can be manufactured.In the case where the cross-sectional shape of the continuous long-fiberprecursor is set to a complete round shape, the lower limit of theaverage fiber diameter is preferably set to 3 μm with the upper limitbeing set to 25 μm, and the lower limit of the average fiber diameter ismore preferably set to 5 μm with the upper limit being set to 15 μm.

Furthermore, it is preferable to carry out a crimping process forapplying a crimp to the above-mentioned continuous long-fiber precursor.This arrangement allows the alumina short fibers to be preferablyentangled with one another, when the alumina short fibers are formedinto a mat shape in the succeeding mat-forming process.

Next, a chopping process is carried out so as to cut the above-mentionedcontinuous long-fiber precursor into a short fiber precursor.

In this chopping process, the above-mentioned continuous long-fiberprecursor is cut in a manner so as to preferably set its lower limit to0.1 mm, more preferably 2 mm, with its upper limit being set to 100 mm,more preferably 50 mm.

More specifically, a plurality of the continuous long-fiber precursorsare aligned side by side, and cut by a rectangular cutter or the like,and in this case, the cutting process is preferably carried out so thatthe cut faces become flat. If the cut face of each short fiber precursorhas an aspire shape, the cut face of the alumina short fiber to beformed later also has an aspire shape, and if these short fiberprecursor and alumina short fibers are inhaled, serious damages might becaused in the human body.

Next, a mat-forming process is carried out so that a mat-shapedshort-fiber precursor is produced by using the resulting short-fiberprecursor.

In this mat-forming process, after the resulting precursor short fibershave been collected, untied and laminated, these are pressed to form amat-shaped short-fiber precursor.

In this mat-shaped short-fiber precursor, the above-mentionedshort-fiber precursor is in an entangled state to a certain degree.

Not particularly limited, the shape of the above-mentioned mat-shapedshort-fiber precursor is normally set to a rectangular shape.

Moreover, the size thereof is appropriately determined in accordancewith the purpose of use of the alumina fiber aggregation.

Next, this mat-shaped short-fiber precursor is preferably subjected to aneedle punch process. In this needle punch process, by sticking a needleinto the above-mentioned mat-shaped short-fiber precursor, the upper andlower short-fiber precursors are preferably entangled so that it ispossible to provide a mat-shaped short-fiber precursor having highbulkiness and elasticity.

Then, the above-mentioned mat-shaped short-fiber precursor is fired in afiring step to manufacture an alumina fiber aggregation, therebycompleting the manufacturing method of the alumina fiber aggregationaccording to the sixth group of the present invention.

In this firing step, first, the above-mentioned mat-shaped short-fiberprecursor is preferably heated (pre-processing) under conditions of 400to 600° C. for 10 to 60 minutes in an oxygen-containing atmosphere. Thisprocess is applied so as to fire and eliminate organic componentscontained in the short fiber precursor used in the mat-shapedshort-fiber precursor.

Next, the mat-shaped short-fiber precursor, which has been subjected tothe above-mentioned pre-processing, is heated to a temperature in theatmosphere, with the lower limit being set to 1000° C., preferably,1050° C., and the upper limit being set to 1300° C., preferably, 1250°C. so that the short-fiber precursor is sintered. The heatingtemperature of less than 1000° C. tends to make the sintering step ofthe short fiber precursor insufficient, making it difficult to obtain analumina fiber aggregation with high strength. In contrast, the heatingtemperature exceeding 1300° C. fails to provide high strength of thealumina fiber aggregation, resulting in disadvantages in theproductivity and economical efficiency.

In this firing step, the short fiber precursor used in the mat-shapedshort-fiber precursor is sintered to be formed into alumina shortfibers, and the above-mentioned precursor short fibers are entangled ina complex manner through the above-mentioned needle punch process andthe like, and then these entangled precursor short fibers are fired soas to be mutually bonded. Thus, the manufactured alumina fiberaggregation is allowed to have excellent mechanical strength.

Moreover, the mat-shaped short-fiber precursor, fired in theabove-mentioned conditions, has its organic components fired andeliminated so that its volume is reduced.

Normally, the above-mentioned alumina short fibers are mainly composedof alumina and silica, and the alumina short fibers are preferably setto have a mullite crystal content of 0 to 10% by weight or less. Sincethe alumina short fibers having such a chemical composition has a smallamorphous component so that it has excellent heat resistance and highrepulsive force upon application of compressing load. Therefore, in thecase where the alumina fiber aggregation according to the sixth group ofthe present invention is used as a holding seal material such as ahoneycomb filter 10 as described in the prior art section, even whenthis is subjected to a high temperature in a state placed in a gapbetween the metal shell and the honeycomb filter 10, it is possible toreduce the possibility of reduction in the face pressure to begenerated.

Moreover, the fiber tensile strength of the above-mentioned aluminashort fiber is preferably set to 1.2 GPa or more, more preferably 1.5Gpa or more. Further, the fiber bending strength of the alumina shortfibers is preferably set to 1.0 GPa or more, more preferably 1.5 GPa ormore. Moreover, the fracture toughness value of the alumina short fibersis preferably set to 0.8 MN/m^(3/2) or more, more preferably 1.3MN/m^(3/2) or more. This is because as the fiber tensile strength, thefiber bending strength and the fracture toughness value increase, thealumina short fibers become very strong against the tension and bending,thereby forming flexible alumina short fibers that are less susceptibleto damage.

Thereafter, the above-mentioned alumina fiber aggregation is formed intoa holding seal material having virtually the same shape as the holdingseal material 30 shown in FIG. 18 by a punching process and the like.

The size of the holding seal material is properly determined inaccordance with the purpose of use, and when used as a holding sealmaterial to be wound around the outer circumference of the honeycombfilter 10, for example, shown in FIG. 16, the thickness of the holdingseal material is set to approximately 1.1 to 4 times the gap between theouter diameter of the honeycomb filter 10 and the inner diameter of themetal shell housing the honeycomb filter 10, more preferablyapproximately 1.5 to 3 times the gap.

The thickness of the holding seal material of less than 1.1 times theabove-mentioned gap fails to provide a high holding property in thehoneycomb filter 10 when the honeycomb filter 10 is housed in the metalshell, resulting in the possibility of deviation and backlash of thehoneycomb filter 10 against the metal shell. Since this case of coursefails to provide a high sealing property, leakage of exhaust gas tendsto occur from the gap portion, causing an insufficient purifyingproperty for exhaust gas. In contrast, if the thickness of the holdingseal material exceeding four times the above-mentioned gap, it becomesdifficult to place the honeycomb filter 10 in the metal shell, inparticular, when a press-fitting system is adopted so as to place thehoneycomb filter 10 in the metal shell.

Moreover, after the holding seal material has been housed in the metalshell, the lower limit of the bulk density thereof is preferably set to0.1 g/cm³, with the upper limit thereof being set to 0.3 g/cm³, and thelower limit of the bulk density of the holding seal material is morepreferably set to 0.1 g/cm³, with the upper limit being set to 0.25g/cm³. The bulk density of less than 0.1 g/cm³ fails to provide asufficiently high initial face pressure of the holding seal material; incontrast, the bulk density exceeding 0.3 g/cm³ increases the quantity ofalumina short fibers to be used as a material, resulting in highmanufacturing costs.

Furthermore, the aforementioned holding seal material may be subjectedto the needle punching process, if necessary, and after the holding sealmaterial has been subjected to an impregnation process in an organicbinder, this may be further compressed and molded in the thicknessdirection of the holding seal material. The application of theseprocesses makes it possible to compress the holding seal material in thethickness direction and consequently to make it thinner.

With respect to the above-mentioned organic binder, PVA and acrylicresins may be used, in addition to latexes and the like such as acrylicrubber and nitrile rubber and the like.

As described above, in the manufacturing method of the alumina fiberaggregation according to the sixth group of the present invention, thealumina-fiber stock solution is subjected to a spinning process, andextended to form a continuous long-fiber precursor, and the resultingcontinuous long-fiber precursor is then cut to form short-fiberprecursors; then, these are formed into a mat precursor so that analumina fiber aggregation is manufactured by sintering this matprecursor.

In accordance with the manufacturing method of the alumina fiberaggregation according to the sixth group of the present invention, thecut surface of the above-mentioned short-fiber precursor is free fromthe generation of chips, burs and micro-cracks, and this is thensubjected to a sintering step so that it is possible to manufacturealumina short fibers that are excellent in the mechanical strength.

In other words, since the alumina short fibers to be used in the aluminafiber aggregation are allowed to have excellent mechanical strength, itbecomes possible to provide an alumina fiber aggregation that has asufficiently high initial face pressure, and is less susceptible todegradation with time in the face pressure.

The following description will be given of more specific examples of theabove-mentioned embodiments, and comparative examples thereof; however,the present invention is not intended to be limited by these examples.

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

The following description will be given of examples and comparativeexamples according to the first group of the present invention.

EXAMPLE 1

In example 1, first, a basic water solution of aluminum chloride (23.5%by weight), silica sol (20% by weight, silica particle size 15 nm) andpolyvinyl alcohol (10% by weight) that is a fiber-drawing propertyapplying agent were mixed to prepare a spinning stock solution. Next,the resulting spinning stock solution was condensed under vacuum at 50°C. by using an evaporator to prepare a spinning stock solution having aconcentration of 38% by weight with a viscosity of 1500 Poise.

After preparation, the spinning stock solution was continuouslydischarged into the air through a nozzle (having a complete round shapein its cross-section) of the spinning device, and the precursor fibersthus formed were wound up while being extended.

Next, after the above-mentioned precursor fibers had been subjected to aheating step (pre-processing) at 250° C. for 30 minutes in an electricfurnace that is maintained at normal pressure in a nitrogen atmosphere,these were sintered at 1250° C. for 10 minutes in an electric furnacethat is maintained at normal pressure in a nitrogen atmosphere in thesame manner.

As a result, a complete-round-shaped alumina-silica based fiber 6 whichhad an alumina-silica weight ratio of 72:28, an average-fiber-size of10.5 μm and a quantity of residual carbon of 5% by weight (see Table 1)was obtained. When the mechanical strengths of this alumina-silica basedfiber 6 were measured by publicly known methods, the fiber tensilestrength was 2.0 GPa, the fiber bending strength was 1.8 GPa, and thefracture toughness was 1.5 MN/m^(3/2). In other words, thealumina-silica based fibers 6 of embodiment 1 had excellent mechanicalstrengths.

When the resulting alumina-silica based fibers 6 were visually observed,the diameter and cross-sectional shape thereof were evenly set and couldbe referred to have excellent stability in quality. Moreover, thealumina-silica based fiber 6 had a black color (so-called carbon blackcolor), which was a novel feature that had not been provided.

Next, the long fiber of the alumina-silica based fiber 6 was choppedinto a length of 5 mm to provide short fibers. Thereafter, these shortfibers were dispersed in water, and the resulting fiber dispersionsolution was poured into a mold, and pressed and dried so that amat-shaped fiber aggregation was obtained. Then, samples were formedfrom this fiber aggregation, and with respect to the face pressure,measuring tests were carried out in the following manner.

First, the fiber aggregation was punched out to a square shape with 25mm in each side to prepare a face-pressure measuring-use sample, andthis was sandwiched by special jigs, and adjusted to have a bulk density(GBD) of 0.30 g/cm³. The face-pressure measuring-use sample in thisstate was held in the atmosphere at 1000° C., and the face pressure wasmeasured 1 hour later, 10 hours later, and 100 hours later. Here, theface pressure which had been measured without heating in anon-sandwiched state was defined as “initial face pressure”, and theface pressure 100 hours later was defined as “face pressure afterendurance tests”. Moreover, the expression, (face pressure afterendurance tests/initial face pressure)×110 (%) was calculated, anddefined as the degradation with time rate of face pressure. Table 1shows the results of these tests.

In accordance with the results of the tests, in the sample of example 1,both of the initial face pressure and the face pressure after endurancetests exceeded 100 kPa, and the degradation with time rate of facepressure was maintained within 50%, which was a comparatively low level.Here, when the sample obtained 100 hours later was observed, it wasfound that the properties of the alumina-silica based fiber 6 were notparticularly changed, and still had a black color. The quantity ofresidual carbon was also maintained at 5% by weight.

Moreover, after the above-mentioned mat-shaped fiber aggregation hadbeen punched out to a predetermined shape, and actually formed into aholding seal material 4, this was wound around a catalyst carrier 2, andthe resulting member 2 was press-fitted into a metal shell 3.

With respect to the catalyst carrier 2, a cordierite monolith having anouter diameter of 130 mmφ and a length of 100 mm was used. With respectto the metal shell 3, a cylinder member, which was made of SUS304 havingan O-letter shape in its cross-section with 1.5 mm in thickness and 140mmφ in inner diameter, was used. A catalyst converter 1, assembled inthis manner, was actually loaded into a gasoline engine of 3 liters, andthis was subjected to a continuous driving test. As a result, upontraveling, neither noise nor backlash of the catalyst carrier 2 wasgenerated so that it was confirmed that the initial face pressure wasimproved, with the degradation with time in the face pressure beingsecurely prevented. Moreover, it was possible to provide an excellentanti-wind erosion property.

EXAMPLES 2, 3

In examples 2, 3, alumina-silica based fibers 6 were respectivelyprepared basically in the same sequence as example 1 except that thefiring temperature and the firing time were changed as shown in Table 1.As a result, it was possible to obtain alumina-silica based fibers 6that were excellent in mechanical strengths.

Moreover, when face-pressure measuring-use samples were formed, and theinitial face pressure, the face pressure after endurance tests and thedegradation with time rate of face pressure were measured on these,preferable results were obtained in the same manner as example 1 (seeTable 1).

Of course, no changes were observed with respect to the color andquantity of residual carbon.

Furthermore, a holding seal material 4 was formed so as to prepare acatalyst converter 1, and a continuous driving test was carried out byloading this. As a result, upon traveling, neither noise nor backlash ofthe catalyst carrier 2 was generated so that it was confirmed that theinitial face pressure was improved, with the degradation with time inthe face pressure being securely prevented.

COMPARATIVE EXAMPLE 1

In comparative example 1, a spinning process was carried out by using aspinning stock solution having the same composition as example 1 so thatprecursor fibers were formed. Next, after the above-mentioned precursorfibers had been subjected to a heating step (pre-processing) at 250° C.for 30 minutes in an electric furnace that is maintained at normalpressure in an active atmosphere containing oxygen (the atmosphere),these were sintered at 1250° C. for 10 minutes in an electric furnacethat is maintained at normal pressure in the same active atmosphere (theatmosphere) in the same manner.

As a result, a complete-round-shaped alumina-silica based fiber 6 with atransparent white color, which had an alumina-silica weight ratio of72:28, an average-fiber-diameter of 10.2 μm and a quantity of residualcarbon of 0% by weight (see Table 1), was obtained. The mechanicalstrengths of this alumina-silica based fiber 6 were shown in Table 1,which indicated approximately half of the values of examples 1 to 3. Inother words, the alumina-silica based fiber 6 of comparative example 1was clearly inferior to those obtained in examples 1 to 3.

Moreover, face-pressure measuring-use samples were prepared so that theinitial face pressure, the face pressure after endurance tests and thedegradation with time rate of face pressure were measured, and it wasconfirmed that these values were clearly inferior to those of examples 1to 3 (see Table 1).

TABLE 1 Comparative Example 1 Example 2 Example 3 Example 1 Firingatmosphere Nitrogen Nitrogen Nitrogen Atmosphere Firing temperature1250° C. 1290° C. 1150° C. 1250° C. Firing time 10 minutes 5 minutes 20minutes 10 minutes Color of fiber Black (5) Black (6) Black (8) White(9) (Brightness) Quantity of residual 3% by weight 5% by weight 1% byweight 0% by weight carbon Average fiber diameter 10.5 μm 10.5 μm 10.5μm 10.2 μm Fiber tensile strength 2.0 Gpa 1.8 Gpa 2.3 Gpa 1.1 Gpa Fiberbending strength 1.8 Gpa 1.6 Gpa 2.0 Gpa 0.9 Gpa Fracture toughness 1.5MN/m^(3/2) 1.6 MN/m^(3/2) 1.5 MN/m^(3/2) 0.7 MN/m^(3/2) Bulk density0.10 g/cm³ 0.10 g/cm³ 0.10 g/cm³ 0.10 g/cm³ Initial face pressure 185kPa 180 kPa 192 kPa 144 kPa Face pressure after 107 kPa 105 kPa 105 kPa35 kPa endurance tests Degradation with time 42.2% 41.7% 45.3% 75.7%rate of face pressure

Next, the following description will be given of examples andcomparative examples according to the second group of the presentinvention.

EXAMPLE 4

In example 4, first, long fibers of precursor fibers were prepared inthe same manner as example 1.

Next, the long fiber of precursor fiber was chopped to a length of 5 mmso that short fibers were prepared. Thereafter, these short fibers weredispersed in water, and the resulting fiber dispersion solution waspoured into a mold, and pressed and dried so that a mat-shaped fiberaggregation M1 was obtained.

In a firing step following the above-mentioned laminating process, afterthe above-mentioned fiber aggregation M1 had been subjected to a heatingstep (pre-processing) at 250° C. for 30 minutes in an electric furnace21 that is maintained at normal pressure in the atmosphere, these weresintered in the electric furnace 21 that is maintained at normalpressure in the atmosphere in the same manner.

In example 4, the temperature of an upper electric heater 24 was sethigher so that the surface temperature on the first face side S1 was setto 1250° C. at the firing time, while the temperature of a lowerelectric heater 25 was set lower so that the surface temperature on thesecond face side S2 was set to 1000° C. In other words, a firingtemperature difference of 250° C. was prepared. The firing time was setto 30 minutes.

The alumina-silica based fibers 6 on the surface layer portion of thefirst face side S1 and the surface layer portion of the second face sideS2 of the fiber aggregation M1 thus obtained were respectively sampled,and these fibers were examined with respect to several points. Table 2shows the test results.

With respect to the crystallization rate of the alumina-silica basedfibers 6, the rate on the surface layer portion of the first face sideS1 was clearly smaller than that on the surface layer portion of thesecond face side S2.

In contrast, with respect to the fiber tensile strength, fiber bendingstrength, elastic modulus and extension rate of the alumina-silica basedfibers 6, those factors on the surface layer portion of the first faceside S1 were clearly greater than those on the surface layer portion ofthe second face side S2.

Here, the weight ratio of alumina-silica was 72:28, the average fiberdiameter was 10.5 μm, and the cross-sectional shape of the fiber had acomplete round shape.

The mat-shaped fiber aggregation M1 was punched out to a square shapewith 25 mm in each side to prepare a face-pressure measuring-use sample,and this was sandwiched by special jigs, and adjusted to have a bulkdensity (GBD) of 0.30 g/cm³. The face-pressure measuring-use sample inthis state was held in the atmosphere at 1000° C., and the face pressurewas measured 1 hour later, 10 hours later, and 100 hours later,respectively. Here, the face pressure which had been obtained 1 hourlater was defined as “initial face pressure”, and the face pressure 100hours later was defined as “face pressure after endurance tests”.Moreover, the expression, (face pressure after endurance tests/initialface pressure)×100 (%) was calculated, and defined as the degradationwith time rate of face pressure. The results of these tests are shown ina graph of FIG. 6.

In accordance with the results of the tests, in the sample of example 4,both of the initial face pressure and the face pressure after endurancetests exceeded 100 kPa, and the degradation with time rate of facepressure was maintained at a comparatively low level.

A catalyst converter 1 was assembled in the same as example 1 by usingthe mat-shaped fiber aggregation M1, and this was loaded into a gasolineengine of 3 liters, and subjected to a continuous driving test. As aresult, upon traveling, neither noise nor backlash of the catalystcarrier 2 was generated so that it was confirmed that the initial facepressure was improved, with the degradation with time in the facepressure being securely prevented. Moreover, no leakage of exhaust gaswas found so that an excellent sealing property was obtained togetherwith an excellent anti-wind erosion property.

COMPARATIVE EXAMPLE 2

In comparative example 2, a firing step was carried out at 1250° C. for30 minutes in an even manner without setting any difference in thefiring temperature. Except for this point, a fiber aggregation M1 wasformed basically under the same conditions as the examples.

In comparative example 2, the physical properties of the alumina-silicabased fiber 6 (the crystallization rate, the fiber tensile strength,fiber bending strength, elastic modulus and extension rate) werevirtually the same as those of the alumina-silica based fibers 6 locatedon the surface layer portion on the second face side S2 of the example.In other words, there was no specific difference in the crystallizationrate, etc. depending on portions.

Moreover, face-pressure measuring-use samples were prepared in the samemanner as the examples, and measurements were carried out on these withrespect to the initial face pressure, face pressure after endurancetests and degradation with time rate of face pressure. As shown in agraph of FIG. 6, the samples of comparative example 2 were clearlyinferior to those of example 4.

TABLE 2 First face side Second face side Firing temperature 1000° C.1250° C. Firing time 30 minutes 30 minutes Crystallization 0.0% byweight 8.3% by weight rate Fiber tensile 2.3 GPa 1.1 Gpa strength Fiberbending 2.0 GPa 0.9 GPa strength Elastic modulus 11.3 × 10¹⁰ N/m² 9.8 ×10¹⁰ N/m² Extension rate 2.3% 1.0%

The following description will be given of examples and comparativeexamples according to the third group of the present invention.

EXAMPLE 5

In example 5, face-pressure-evaluation-use samples of a holding sealmaterial 4 were formed in the following manner.

First, a basic water solution of aluminum chloride (23.5% by weight),silica sol (20% by weight, silica particle size 15 nm), polyvinylalcohol (10% by weight) and tetraethylene glycol monobutylether (1% byweight) were mixed to prepare a spinning stock solution 18. Next, theresulting spinning stock solution 18 was condensed under vacuum at 50°C. by using an evaporator to prepare a spinning stock solution 18 havinga concentration of 38% by weight with a viscosity of 1000 Poise.

After preparation, the spinning stock solution 18 was supplied to aspinning device 20 of FIG. 8. The shape of a metal mouth 19 a of thenozzle 19 was set to a rectangular shape (longer side: 500 μm, shorterside: 50 μm), as shown on the 1^(st) row in the left column of the tableof FIG. 9. During the spinning process, dry hot air of 10 m/s at 50° C.was continuously discharged from a dry-air discharging port.

Thus, the spinning stock solution 18 was continuously discharged intothe air through the metal mouth 19 a so that a precursor fiber 6A wasformed, and the precursor fiber 6A thus formed was wound up while beingextended. At this time, dry hot air was blown to the precursor fibers 6in the forward direction of the discharging direction thereof so thatthe drying process and extending process were carried outsimultaneously.

Next, after the above-mentioned precursor fibers 6A had been subjectedto a heating step (pre-processing) at 250° C. for 30 minutes in anelectric furnace that is maintained in the air atmosphere, these weresintered at 1200° C. for 10 minutes in an electric furnace in the samemanner.

As a result, as shown on the 1^(st) row in the right column of the tableof FIG. 9 and FIG. 10, an alumina-silica based fiber 6 (average majoraxis: 15 μm, average minor axis: 10 μm) which had an ellipticalcross-section according to example 5, was obtained. This alumina-silicabased fiber 6 had a mullite crystal content of approximately 8% byweight and an alumina-silica weight ratio of 72:28. Here, hardly anyorganic substances were contained in the components of thealumina-silica based fiber 6. Moreover, FIG. 10 shows an SEM photographthat indicates a cross-section of the alumina-silica based fiber 6according to example 5.

Next, the long fiber of the alumina-silica based fiber 6 was choppedinto a length of 5 mm to provide short fibers. Thereafter, these shortfibers were dispersed in water, and the resulting fiber dispersionsolution was poured into a mold, and pressed and dried so that amat-shaped fiber aggregation having a thickness of 20 mm was obtained.This was then punched out to a square shape with 25 mm in each side toprepare a face-pressure evaluation sample of example 5.

In the face-pressure evaluation test, the above-mentioned sample wascompressed to a thickness of 3 mm by using a compressing jig, and thisprocess was repeated five times. In this case, the face pressure valueat the time of the first compression and the face pressure value at thetime of the fifth compression were measured, and based upon the resultsof the measurements, the rate of residual face pressure (%), which formsan index of the degree of degradation with time in face pressure, wasfound. The result of this was 95.0% as shown in Table 3.

After this fiber aggregation had been punched out to a predeterminedshape and formed into a holding seal material 4, this was wound around acatalyst carrier 2, and the resulting member 2 was press-fitted into ametal shell 3. With respect to the catalyst carrier 2, a cordieritemonolith having an outer diameter of 130 mmφ and a length of 100 mm wasused. With respect to the metal shell 3, a cylinder member, which wasmade of SUS304 having an O-letter shape in its cross-section with 1.5 mmin thickness and 140 mmφ in inner diameter, was used. A catalystconverter 1, assembled in this manner, was actually loaded into agasoline engine of 3 liters, and this was subjected to a continuousdriving test. As a result, upon traveling, neither noise nor backlash ofthe catalyst carrier 2 was generated even after a lapse of considerablylong time so that it was confirmed that the degree of degradation withtime in the face pressure was reduced.

EXAMPLE 6

In example 6, the same sequence as example 5 was basically carried outexcept that the shape of the metal mouth 19 a was changed. As a result,an alumina-silica based fiber 6 (average major axis: 30 μm, averageminor axis: 10 μm) which had an elliptical cross-section according toexample 6, was obtained. This alumina-silica based fiber 6 had a mullitecrystal content of approximately 8% by weight and an alumina-silicaweight ratio of 72:28. Here, hardly any organic substances werecontained in the components of the alumina-silica based fiber 6.

Next, the mat-shaped fiber aggregation was punched out to a square shapewith 25 mm in each side to prepare a face-pressure evaluation sample ofexample 6, and this was subjected to a face-pressure evaluation test inthe same manner as example 1. As a result, in Example 6, the residualrate of 94.0% was obtained (see FIG. 3).

Moreover, a holding seal material 4 was prepared, and a catalystconverter 1 was assembled, and this was then actually loaded into agasoline engine of 3 liters, and subjected to a continuous driving test.As a result, upon traveling, neither noise nor backlash of the catalystcarrier 2 was generated even after a lapse of considerably long time sothat it was confirmed that the degree of degradation with time in theface pressure was reduced.

EXAMPLE 7

In example 7, the same sequence as example 5 was basically carried outexcept that the shape of the metal mouth 19 a was formed into avirtually dumbbell shape having a size as shown on the second row in theleft column of the table of FIG. 9. As a result, as shown on the secondrow in the right column of FIG. 9 and FIG. 11, an alumina-silica basedfiber 6 (average width: 20 μm, average center thickness: 5 μm, averageedge portion thickness: 10 μm) which had a cocoon shaped cross-sectionor a virtually peanut-shaped cross-section according to example 7 wasobtained. This alumina-silica based fiber 6 had a mullite crystalcontent of approximately 8% by weight and an alumina-silica weight ratioof 72:28. Here, hardly any organic substances were contained in thecomponents of the alumina-silica based fiber 6. Further, FIG. 11 is anSEM photograph that shows a cross-section of the alumina-silica basedfiber according to example 7.

Next, the mat-shaped fiber aggregation was punched out to a square shapewith 25 mm in each side to prepare a face-pressure evaluation sample ofexample 2, and this was subjected to a face-pressure evaluation test inthe same manner as example 5. As a result, in example 7, the residualrate of 89.9% was obtained (see FIG. 3).

Moreover, a holding seal material 4 was prepared, and a catalystconverter 1 was assembled, and this was then actually loaded into agasoline engine of 3 liters, and subjected to a continuous driving test.As a result, upon traveling, neither noise nor backlash of the catalystcarrier 2 was generated even after a lapse of considerably long time sothat it was confirmed that the degree of degradation with time in theface pressure was reduced.

EXAMPLE 8

In example 8, the same sequence as example 5 was basically carried outexcept that the shape of the metal mouth 19 a was formed into avirtually C-letter shape having a size as shown on the third row in theleft column of the table of FIG. 9. As a result, as shown on the thirdrow in the right column of FIG. 9, an alumina-silica based fiber 6having a hollow cross-sectional shape (outer diameter: 20 μm, innerdiameter: 10 μm) according to example 8 was obtained. Thisalumina-silica based fiber 6 had a mullite crystal content ofapproximately 8% by weight and an alumina-silica weight ratio of 72:28.Here, hardly any organic substances were contained in the components ofthe alumina-silica based fiber 6.

Next, the mat-shaped fiber aggregation was punched out to a square shapewith 25 mm in each side to prepare a face-pressure evaluation sample ofexample 8, and this was subjected to a face-pressure evaluation test inthe same manner as example 1. As a result, in example 8, the residualrate of 94.6% was obtained (see FIG. 3).

Moreover, a holding seal material 4 was prepared, and a catalystconverter 1 was assembled, and this was then actually loaded into agasoline engine of 3 liters, and subjected to a continuous driving test.As a result, upon traveling, neither noise nor backlash of the catalystcarrier 2 was generated even after a lapse of considerably long time sothat it was confirmed that the degree of degradation with time in theface pressure was reduced.

TEST EXAMPLE 1

In test example 8, the same sequence as example 5 was basically carriedout except that the shape of the metal mouth 19 a was changed. As aresult, an alumina-silica based fiber 6 having an ellipticalcross-sectional shape (average major axis: 35 μm, average minor axis: 10μm) according to test example 1 was obtained. This alumina-silica basedfiber 6 had a mullite crystal content of approximately 8% by weight andan alumina-silica weight ratio of 72:28. Here, hardly any organicsubstances were contained in the components of the alumina-silica basedfiber 6.

Next, the mat-shaped fiber aggregation was punched out to a square shapewith 25 mm in each side to prepare a face-pressure evaluation sample oftest example 1, and this was subjected to a face-pressure evaluationtest in the same manner as example 1. As a result, in test example 1,the residual rate of 92.0% was obtained (see FIG. 3).

However, it was found that its initial face pressure was lower incomparison with the respective examples.

COMPARATIVE EXAMPLE 3

In comparative example 3, the same sequence as example 5 was basicallycarried out except that the shape of the metal mouth 19 a was formedinto a complete round shape having a diameter of 0.2 mm as shown on thefourth row in the left column of the table of FIG. 9. As a result, asshown on the fourth row in the right column of FIG. 9, an alumina-silicabased fiber 6 having a complete round cross-sectional shape (outerdiameter: 10 μm) according to comparative example 3 was obtained. Thisalumina-silica based fiber 6 having a complete round cross-sectionalshape of comparative example 3 had a mullite crystal content ofapproximately 8% by weight and an alumina-silica weight ratio of 72:28.Here, hardly any organic substances were contained in the components ofthe alumina-silica based fiber 6.

Next, the mat-shaped fiber aggregation was punched out to a square shapewith 25 mm in each side to prepare a face-pressure evaluation sample ofcomparative example 3, and this was subjected to a face-pressureevaluation test in the same manner as example 5. As a result, incomparative example 3, the residual rate was 85.0%, which was clearlyinferior to the respective examples (see FIG. 3).

Therefore, it was found that the degree of degradation with time in facepressure would be greater in comparison with the respective examples.

TABLE 3 Face Face pressure pressure Fiber sectional value in value inResidual shape the first time the fifth time rate Example 5 Ellipticalshape 202 kPa 192 kPa 95.0% Example 6 Elliptical shape 200 kPa 188 kPa94.0% Example 7 Cocoon shape 208 kPa 187 kPa 89.9% Example 8 Hollowshape 205 kPa 194 kPa 94.6% Comparative Complete round 213 kPa 181 kPa85.0% Example 3 shape

The following description will be given of examples and comparativeexamples according to the fourth group of the present invention.

EXAMPLE 9

In example 9, face-pressure-evaluation-use samples of a holding sealmaterial 4 were formed in the following manner.

First, a basic water solution of aluminum chloride (23.5% by weight),silica sol (20% by weight, silica particle size 15 nm), polyvinylalcohol (10% by weight) and an antifoamer (n-octanol) were mixed toprepare a spinning stock solution. Next, the resulting spinning stocksolution was condensed under vacuum at 50° C. by using an evaporator toprepare a spinning stock solution having a concentration of 38% byweight with a viscosity of 1000 to 2000 Poise.

The spinning stock solution, thus prepared, was continuously dischargedinto the air through the nozzle of a spinning device, and the precursorfiber thus formed was wound up while being extended.

At this time, in order to control the fiber diameter, the followingconditions were set. In other words, the diameter of the nozzledischarging port was set to 0.1 to 0.2 mm, the length was set to 0.3 to2.0 mm, and the discharging rate was set to 1.5 to 2.0 cm/s; thus, thespinning stock solution was discharged. After the precursor fiberderived from the spinning stock solution had been extended at a rate 100to 200 times the above-mentioned discharging rate, the fiber was woundaround a winder having a diameter of approximately 12 cm. A cylinderhaving a length of 2 to 4 m was placed between the nozzle dischargingport and the winder, and the precursor fiber was allowed to pass throughthe cylinder. The upper half of the inside of the cylinder was set to atemperature of 35 to 40° C., and the lower half of the inside of thecylinder was set to a temperature of 25 to 30° C.

Successively, the long fiber of the precursor fiber was chopped to alength of 10 mm by using a guillotine cutter so that short fibers wereprepared. Thereafter, these short fibers (approximately 1.0 g) weredispersed in water, and the resulting fiber dispersion solution waspoured into a mold, and pressed and dried so that a mat-shaped fiberaggregation having a square shape with 25 mm in the longitudinal andlateral sides was obtained.

Next, after the above-mentioned mat-shaped fiber aggregation had beensubjected to a heating step (pre-processing) at 250° C. for 30 minutesin an electric furnace that is maintained in the air atmosphere, thiswas sintered at 1250° C. for 10 minutes in an electric furnace in thesame manner.

As a result, a sample of the holding seal material 4, made from thecomplete-round-shaped alumina-silica based fiber 6 that had a mullitecrystal content of approximately 8% by weight and an alumina-silicaweight ratio of 72:28, was obtained.

Alumina-silica based fibers 6 were taken from a plurality of portions ofthe sample of example 9 thus obtained, and the average fiber diameter(μm) and the minimum, maximum and average fiber length (mm) thereof aswell as the minimum value, maximum value and shot content (%) wereexamined. Table 4 shows the results of the measurements. In accordancewith these values, in example 9, dispersions in the fiber diameter anddispersions in the fiber length were extremely small so that it wasconfirmed that these values are maintained within the above-mentionedpreferable ranges. Moreover, no shot was contained in the sample.

Next, a plurality of samples having a square shape with 25 mm in eachside were punched out from a large one sheet of mat-shaped fiberaggregation, and the basis weight was examined from each of these basedupon the area and weight thereof, and the face pressure thereof wasmeasured by using an autograph. Table 4 also shows the results of these.Here, the measured face pressure values were based upon the dataobtained when GBD was set to 0.30 g/cm³. These values showed that inexample 9, dispersions in the basis weight and dispersions in the facepressure were small, indicating stability in quality. Moreover, it wasalso found that the average face pressure value became higher.

COMPARATIVE EXAMPLE 4

In comparative example 4, the same spinning stock solution as example 9was condensed under vacuum at 50° C. by using an evaporator to prepare aspinning stock solution having a concentration of 38% by weight with aviscosity of 10 to 100 Poise.

With respect to the spinning device, a disc-shaped centrifugal nozzle,which has a diameter of 50 to 100 mm with discharging holes of 0.2 to0.8 mm being placed at 16 positions with equal intervals, was used.Then, by using a centrifugal force exerted when this nozzle was rotatedat the number of revolutions of 1000 to 2000 rpm, the spinning stocksolution was discharged, and formed into fibers. Moreover, the resultingprecursor fibers were blown by air in 0.5 to 1.0 kPa at 30° C.,collected, and laminated to form a mat-shaped fiber aggregation. Thiswas molded into a square shape with 25 mm in the longitudinal andlateral sides, and subjected to the same pre-processing and firing stepin the same conditions as example 9 to be formed into ceramics.

Alumina-silica based fibers 6 were taken from a plurality of portions ofthe sample of comparative example obtained by such a blowing method, andthe average fiber diameter (μm) and the minimum, maximum and averagefiber length (mm) thereof as well as the minimum value, maximum valueand shot content (%) were examined. Table 4 shows the results of themeasurements. In accordance with these values, with respect tocomparative example 4, it was confirmed that dispersions in the fiberdiameter and dispersions in the fiber length became considerably greaterin comparison with the examples. Moreover, the shots of 3% by weight ormore were contained in the sample.

Next, a plurality of samples having a square shape with 25 mm in eachside were punched out from a large one sheet of mat-shaped fiberaggregation, and the basis weight was examined from each of these basedupon the area and weight thereof, and the face pressure thereof wasmeasured by using an autograph. Table 1 also shows the results of these.Here, the face pressure measured values were based upon the dataobtained when GBD was set to 0.30 g/cm³. These values showed that incomparative example 4, dispersions in the basis weight and dispersionsin the face pressure were greater in comparison with example 9,indicating instability in quality. Moreover, it was also found that theaverage face pressure value was considerably lower than that of example9.

TABLE 4 Comparative Example 8 Example 4 Average fiber diameter 7.1 μm6.8 μm Lower limit value of fiber 4.8 μm 1.1 μm diameter (−2.3 μm) (−5.7μm) Upper limit value of fiber 9.2 μm 22.3 μm diameter (+2.1 μm) (+15.5μm) Average fiber length 10 mm 26 mm Lower limit value of fiber 9 mm 2mm length (−1 mm) (−24 mm) Upper limit value of fiber 11 mm 60 mm length(+1 mm) (+34 mm) Shot content 0.0% by weight 3.8% by weight Averagebasis weight 1152 g/m² 1147 g/m² Lower limit value of basis 1093 g/m²1012 g/m² weight (−59 g/m²) (−135 g/m²) Upper limit value of basis 1183g/m² 1251 g/m² weight (+31 g/m²) (+104 g/m²) Average face pressure 212kPa 154 kPa Lower limit value of face 201 kPa 123 kPa pressure (−11 kPa)(−31 kPa) Upper limit value of face 218 kPa 178 kPa pressure (+6 kPa)(+24 kPa) *Values inside parentheses indicate a difference from theaverage value.

The following description will be given of examples and comparativeexamples according to the fifth group of the present invention.

EXAMPLE 10

In example 10, samples for face pressure evaluation of a holding sealmaterial 4 were formed in the following manner.

First, a basic water solution of aluminum chloride (23.5% by weight),silica sol (20% by weight, silica particle size 15 nm), polyvinylalcohol (10% by weight) and an antifoamer (n-octanol) were mixed toprepare a spinning stock solution. Next, the resulting spinning stocksolution was condensed under vacuum at 50° C. by using an evaporator toprepare a spinning stock solution having a concentration of 38% byweight with a viscosity of 1000 Poise.

The spinning stock solution, thus prepared, was continuously dischargedinto the air through a nozzle of a spinning device, and the precursorfiber thus formed was wound up while being extended.

After the above-mentioned precursor fiber had been subjected to aheating step (pre-processing) at 250° C. for 30 minutes in an electricfurnace that is maintained in the air atmosphere, this was sintered at1250° C. for 10 minutes in an electric furnace in the same manner.

As a result, complete-round-shaped alumina-silica based fibers 6 havingan average fiber diameter of 9 μm, which had a mullite crystal contentof approximately 8% by weight and an alumina-silica weight ratio of72:28, were obtained.

Successively, the long fiber of the precursor fiber 6 was chopped to alength of 5 mm by using a guillotine cutter so that short fibers wereprepared. Thereafter, these short fibers (approximately 1.0 g) weredispersed in water, and the resulting fiber dispersion solution waspoured into a mold, and pressed and dried so that a mat-shaped fiberaggregation having a square shape with 25 mm in the longitudinal andlateral sides was obtained.

Then, after this fiber aggregation had been impregnated with a 5% byweight low-viscosity water solution (1 Centipoise) of aluminum chloridefor approximately 1 to 60 seconds, the resulting fiber aggregation washeated and dried at 100° C. for 10 minutes or more. Further, the driedfiber aggregation was sintered at a temperature of 1200° C. or more for10 minutes so that a cross-linking bridge formed by a ceramic adhesive 7mainly made from alumina was formed at adjacent portions of the shortfibers. FIG. 14 shows an SEM photograph that indicates alumina-silicabased fibers 6 of the present example 10 which were bonded to each otherby the ceramic adhesive 7.

This fiber aggregation was used as a face-pressure-evaluation sample,and the sample was housed inside compressing jig of an autograph. Then,a pressing force was applied to the sample in the thickness direction,and when this had been pressed to 3 mm in thickness, the face pressure(MPa) was measured 1 hour later, 10 hours later and 100 hours later. Theresults are shown in a graph of FIG. 13.

COMPARATIVE EXAMPLE 5

In comparative example 5, a face-pressure-evaluation sample was preparedbasically in the same manner as example 10, except that no bondingprocess was carried out. Then, face-pressure-evaluation tests werecarried out in the same manner as example 10 by using an autograph. Theresults are shown in a graph of FIG. 13.

(Results of Tests)

In accordance with the graphs in FIG. 13, with respect to the initialface pressure, example 10 had a higher value than comparative example 5.Further, with respect to the degree of degradation in face pressureafter a lapse of 100 hours, example 10 was clearly smaller thancomparative example 5.

Moreover, in example 10, after the above-mentioned fiber aggregation hadbeen punched out to a predetermined shape and formed into a holding sealmaterial 4, this was wound around a catalyst carrier 2, and theresulting member 2 was press-fitted into a metal shell 3. With respectto the catalyst carrier 2, a cordierite monolith having an outerdiameter of 130 mmφ and a length of 100 mm was used. With respect to themetal shell 3, a cylinder member, which was made of SUS304 having anO-letter shape in its cross-section with 1.5 mm in thickness and 140 mmφin inner diameter, was used. A catalyst converter 1, assembled in thismanner, was actually loaded into a gasoline engine of 3 liters, and thiswas subjected to a continuous driving test. As a result, upon traveling,neither noise nor backlash of the catalyst carrier 2 was generated.

Here, tests were carried out, in which the alumina-silica based fibers 6obtained from the manufacturing method of the second embodimentaccording to the fifth group of the present invention and thealumina-silica based fibers 6 obtained from the manufacturing method ofthe first embodiment according to the fifth group of the presentinvention were compared with each other, with respect to the fiberdiameter and mechanical strength thereof. The specific testing methodthereof is shown below.

In the former case, 10 fibers were arbitrarily sampled from the shortfibers cut to a predetermined length, and these were sintered to formalumina-silica based fibers 6. Then, the average value of the fiberdiameter and the standard deviation of the 10 alumina-silica basedfibers 6 were examined. As a result, the average value was 7.1 μm andthe standard deviation was 0.74 μm. Moreover, 10 alumina-silica basedfibers 6 were subjected to a publicly known tensile strength test sothat the average value and the standard deviation of the absolutestrength were examined. As a result, the average value was 6.19 gf, andthe standard deviation was 1.88 gf. Furthermore, the average value andthe standard deviation of the relative strength were examined from thedata of the above-mentioned tensile strength test. As a result, theaverage value was 1.40 GPa, and the standard deviation was 0.45 GPa.

In the latter case, a long fiber of the sintered alumina-silica basedfiber 6 was cut to a predetermined length to obtain short fibers, and 10fibers were arbitrarily sampled from these. Then, the average value ofthe fiber diameter and the standard deviation of the 10 alumina-silicabased fibers 6 were examined. As a result, the average value was 7.2 μmand the standard deviation was 0.52 μm. Moreover, 10 alumina-silicabased fibers 6 were subjected to a publicly known tensile strength testso that the average value and the standard deviation of the absolutestrength were examined. As a result, the average value was 4.86 gf, andthe standard deviation was 2.16 gf. Furthermore, the average value andthe standard deviation of the relative strength were examined from thedata of the above-mentioned tensile strength test. As a result, theaverage value was 1.22 GPa, and the standard deviation was 0.61 GPa.

The above-mentioned results show that the alumina-silica based fibers 6of the second embodiment according to the fifth group of the presentinvention are not only excellent in mechanical strength, but alsosmaller in mechanical dispersions, in comparison with the example of thefirst embodiment according to the fifth group of the present invention.Therefore, the application of the alumina-silica based fibers 6 obtainedas described above makes it possible to provide a holding seal material4 having even quality.

The following description will be given of examples and comparativeexamples according to the sixth group of the present invention.

EXAMPLE 11

First, a basic water solution of aluminum chloride (23.5% by weight),silica sol (20% by weight, silica particle size 15 nm) and polyvinylalcohol (10% by weight) that serves as a fiber-drawing property applyingagent were mixed to prepare a spinning stock solution. Next, theresulting spinning stock solution condensed under vacuum at 50° C. byusing an evaporator to prepare a spinning stock solution having aconcentration of 38% by weight with a viscosity of 150 Pa·s (1500 P).

The alumina fiber spinning stock solution, thus prepared, wascontinuously discharged into the air through a nozzle (having a completeround cross-sectional shape) of a spinning device, and wound up whilebeing extended so that a continuous long fiber precursor was formed.

Next, the continuous long precursor fiber was cut to a length of 7.5 mmby using a rectangular-shaped cutter so that short fibers were prepared,and after having been untied, collected and laminated, these shortfibers were pressed so that a mat-shaped fiber aggregation was obtained.

Next, after the above-mentioned mat-shaped fiber aggregation had beensubjected to a heating step (pre-processing) at 500° C. for 30 minutesin an electric furnace that is maintained at normal pressure in the airso that organic components were burnt and eliminated, this was sinteredat 1250° C. for 10 minutes in an electric furnace that was maintained atnormal pressure in the atmosphere to prepare an alumina fiberaggregation.

The above-mentioned alumina fiber aggregation had an alumina-silicaweight ratio of 72:28, was obtained, and the average fiber diameter ofthe alumina short fibers was 7.3 μm with a complete roundcross-sectional shape.

COMPARATIVE EXAMPLE 6

After a continuous long-fiber precursor had been prepared in the samemanner as example 11, the continuous long-fiber precursor was subjectedto a sintering step in the same firing conditions as example 11 so thatan alumina long fiber was prepared. The average fiber diameter of thealumina long fiber was 7.2 μm.

Next, the continuous long precursor fiber was cut to a length of 5 mm byusing a rectangular-shaped cutter so that alumina short fibers wereprepared, and after having been untied, collected and laminated, theseshort fibers were pressed so that a mat-shaped fiber aggregation wasobtained.

The respective physical properties of the alumina fiber aggregations inaccordance with example 11 and comparative example 6 were evaluated byusing the following methods, and the results are shown in the followingTable 5.

(1) Strength of Alumina Short Fibers

The tensile strength of the alumina short fibers used in each of thealumina fiber aggregations in example 11 and comparative example 6 wasmeasured by a tensile tester. The measurements were carried out on tenalumina short fibers that had been arbitrarily sampled, and the averagevalue was determined as the strength of each of the alumina short fibersaccording to example 11 and comparative example 6, and the dispersionsthereof were evaluated based upon the standard deviation.

(2) Measurements on Face Pressure

Each of the fiber aggregations according to example 11 and comparativeexample 6 was punched out to a square shape with 25 mm in each side toprepare a face-pressure measuring-use sample, and the face pressure ofthe face-pressure measuring-use sample in a non-sandwiched state withouta heating step was measured as “initial face pressure”, and theabove-mentioned face-pressure measuring-use sample was sandwiched byspecial jigs, and adjusted to have a bulk density of 0.30 g/cm³, andthen held in the atmosphere at 1000° C.; thus, the face pressuremeasured 100 hours later was defined as “face pressure after endurancetests”.

Moreover, the expression, [100−(face pressure after endurancetests/initial face pressure)×100] (%), was calculated to find thedegradation with time rate of face pressure.

(3) Observation on Cut Face

States of the cut face of the alumina short fibers according to example11 and comparative example 6 were observed by using a scanning electronmicroscope (SEM) so as to examine any chips, burs, micro-cracks and thelike.

TABLE 5 Average fiber diameter Strength of alumina short fiber (μm)Average strength (N) Dispersion Example 10 7.3 6.3 × 10⁻⁴ 1.88Comparative Example 6 7.2 5.0 × 10⁻⁴ 2.16 Face pressure (kPa)Degradation Initial face Face pressure after with time pressureendurance tests test (%) Example 10 145 102 29.7 Comparative Example 6140 91 35 Presence or absence of chips, burs and micro-cracks Example 10Absence Comparative Example 6 Presence

As clearly shown by the results in Table 5, the average fiber strengthof the alumina short fibers according to example 11 was 6.3×10⁻⁴ N withits standard deviation being set to 1.88, while the average fiberstrength of the alumina short fibers according to comparative example 6was 5.0×10⁻⁴ N with its standard deviation being set to 2.16. Thealumina short fibers according to example 11 was superior to the aluminashort fibers according to comparative example 6 in the average strengthand dispersion thereof.

The initial face pressure of the face-pressure measuring-use sampleaccording to example 11 was 145 kPa with the face pressure afterendurance tests being set to 102 kPa, while the initial face pressure ofthe face-pressure measuring-use sample according to comparative example6 was 140 kPa with the face pressure after endurance tests being set to91 kPa; thus, in both of the face pressures, the sample according toexample 11 had better results.

Moreover, with respect to the degradation with time rate of theface-pressure measuring-use sample also, the sample according to example11 had better results.

Furthermore, none of chips, burs and micro-cracks were found on the cutface of the alumina short fiber according to example 11; however, anumber of chips, burs and micro-cracks were observed on the cut face ofthe alumina short fiber according to comparative example 6.

INDUSTRIAL APPLICABILITY

As described above in detail, in accordance with the inventionsaccording to the first group of the present invention, since it ispossible to achieve excellent mechanical strength, it becomes possibleto provide alumina-silica based fibers that are suitable for obtaining aholding seal material which has a high initial face pressure, and isless susceptible to degradation with time in the face pressure.

In accordance with the invention according to the first group of thepresent invention, it is possible to provide a manufacturing methodwhich can securely provide alumina-silica based fibers that areexcellent in mechanical strength easily.

In accordance with the invention according to the first group of thepresent invention, it is possible to obtain the above-mentioned fibersat low costs in a stable manner.

In accordance with the invention according to the first group of thepresent invention, it is possible to maintain basic physical propertiesof the fibers while reducing costs.

In accordance with the invention according to the first group of thepresent invention, it is possible to provide a holding seal materialwhich has a high initial face pressure, and is less susceptible todegradation with time in the face pressure.

In accordance with the invention according to the first group of thepresent invention, it is possible to provide a catalyst-converter-useholding seal material which has a high initial face pressure, and isless susceptible to degradation with time in the face pressure.

In accordance with the invention according to the second group of thepresent invention, it is possible to provide a holding seal materialwhich has a high initial face pressure, is less susceptible todegradation with time in the face pressure, and is also excellent in thesealing property.

In accordance with the invention according to the second group of thepresent invention, it is possible to provide a manufacturing method thatis suitable for obtaining a holding seal material according to thesecond group of the present invention.

In accordance with the invention according to the second group of thepresent invention, it is possible to provide a catalyst converter whichhas a high initial face pressure, is less susceptible to degradationwith time in the face pressure, and is also excellent in the sealingproperty.

In accordance with the inventions according to the third group of thepresent invention, it is possible to provide a holding seal materialthat is less susceptible to degradation with time in the face pressure.

In accordance with the invention according to the third group of thepresent invention, it is possible to provide a manufacturing method thatis suitable for obtaining a holding seal material according to the thirdgroup of the present invention.

In accordance with the invention according to the fourth group of thepresent invention, it is possible to provide a holding seal materialthat is excellent in quality stability.

In accordance with the invention according to the fourth group of thepresent invention, it is possible to provide a manufacturing method thatis suitable for obtaining a holding seal material according to thefourth group of the present invention.

In accordance with the inventions according to the fifth group of thepresent invention, it is possible to provide a holding seal materialthat is less susceptible to degradation with time in the face pressure.

In accordance with the invention according to the fifth group of thepresent invention, it is possible to provide a manufacturing method thatis suitable for obtaining a holding seal material according to the fifthgroup of the present invention.

In accordance with the invention according to the fifth group of thepresent invention, it is possible to provide a ceramic fiber aggregationthat is suitable for the above-mentioned excellent holding sealmaterial, etc. according to the fifth group of the present invention.

In accordance with the invention according to the fifth group of thepresent invention, it is possible to provide a ceramic fiber aggregationthat is suitable for the above-mentioned excellent holding sealmaterial, etc. according to the fifth group of the present invention.

In accordance with a manufacturing method of an alumina fiberaggregation according to the sixth group of the present invention, it ispossible to make the strength of alumina short fibers used in thealumina fiber aggregation superior, and also to reduce the dispersionsthereof. Therefore, it is possible to manufacture an alumina fiberaggregation which has a high initial face pressure, and is lesssusceptible to the degradation with time.

1. A holding seal material which has alumina-silica based fibers aggregated into a mat shape as a constituent element, and is placed in a gap between a ceramic body capable of allowing a fluid to flow through the inside thereof and a metal shell covering the outer circumference of the ceramic body, wherein a crystallization rate is made different depending on portions of the holding seal material, and an outer portion of the holding seal material disposed with respect to the metal shell is crystallized at a lower rate than an inner portion of the holding seal material disposed with respect to the ceramic body.
 2. The holding seal material according to claim 1, wherein the crystallization rate in a portion on a first face side is different from that in a portion on a second face side.
 3. The holding seal material according to claim 1, wherein the crystallization rate is gradually increased from a first face side toward a second face side.
 4. The holding seal material according to claim 1, comprising a sheet of fiber aggregation, wherein the crystallization rate of the fiber aggregation is gradually increased from a first face side toward a second face side.
 5. The holding seal material according to claim 1, wherein the difference between the crystallization rates in the outer portion on a first face side and that in the inner portion on a second face side is 3% by weight or more.
 6. The holding seal material according to claim 1, wherein the crystallization rate in the outer portion on a first face side is 0 to 1% by weight, and the crystallization rate in the inner portion on a second face side is 1 to 10% by weight.
 7. The holding seal material according to claim 1, wherein the ceramic body includes a catalyst carrier, and the holding seal material is used as a holding seal material for a catalyst converter.
 8. The holding seal material according to claim 1, wherein the holding seal material is placed in the gap in such a state that a first face side having a relatively small crystallization rate is made in contact with the metal shell, and a second face side having a relatively large crystallization rate is made in contact with the ceramic body.
 9. The holding seal material according to claim 1, wherein the crystallization rate of the inner portion is 5% by weight or less. 